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TEXT-BOOKS OF SCIENCE 



ADAPTED FOX THE USE OF 



LRTISANS and students in public and science schools 



ELECTRO-METALLURGY 






LONDON : PRINTED BY 

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Frontispiece 




gramme's electrotyping magneto-electric macitne 



5^V 



THE ART 

OF 

ELECTRO-METALLURGY 

INCLUDING ALL KNOWN PROCESSES OF 
ELECTRO-DEPOSITION 



BY g/G0RE, LL.D., F.R.S. 



SECOND EDITION 



D. APPLETON AND CO. 

NEW YORK 

1884 






\1 



D 



oft' 



, 



13 



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INTRODUCTION. 



HAVING been asked by the publishers of the Text- 
books of Science, to write a small volume on the 
subject of Electro-metallurgy, I have endeavoured 
to produce such a book as would be useful to scientific 
students, to practical workers in the art of electro- 
metallurgy, gilders, platers, &c, and to all persons who 
wish to obtain in a compact form, an explanation of 
the principles and facts upon which the art of electro- 
metallurgy is based, the circumstances under which 
nearly every known metal is deposited, and the special 
details of technical workshop manipulation in the 
galvano-plastic art. I have also given an historical 
sketch of the development of the subject, arranged in 
chronological order. 

The book is divided essentially into four parts, 
viz., First, the Historical sketch, sIioa ing how from 
one or two isolated, and apparently unimportant facts, 
the great subject of Electro-chemistry arose, and by 
the incessant, and unremunerated labours of many 



viii Introduction. 

eminent scientific investigators, and the exertions of 
practical operators, it has gradually extended, until 
nearly every known metal has been separated, copper 
has been deposited in great quantities, and the emi- 
nently useful, and beautiful products of artistic 
electro-deposition, have spread nearly all over the 
Earth, and are to be found in every civilised home. 
The Second part consists of the Theoretical division, j) 
being a concise statement of the chief facts and prin- 
ciples upon which the practical art is based, together 
with descriptions of the classes of phenomena usually 
met with in electrolytic and electro-depositing pro- 
cesses ; the facts and principles being arranged in as \ 
systematic and logical an order as I could place them. 
The Third part (section A) is the first portion of the 
Practical division of the book ; and treats of the general 
methods of deposition, the selection of depositing pro- 
cesses, the general rules to be obeyed, and points to 
be observed, in actual working with all metals, followed 
by the special means of depositing nearly every known 
metal and metalloid. The metals, &c, are arranged 
in their ordinary chemical classes in the following 
order : — Electro-negative or brittle metals, noble, base, 
earth and alkaline earth, alkali metals, and finally the 
metalloids ; and the arrangement is such, that every 
known instance of the electro-deposition of nearly 
every known metal, and metalloid, may be readily 
found and referred to. It is hoped that not only 
students and practical workers in the art, will find this 



■Introduction. ix 

) section of value to them, but that even scientific 
investigators may find it useful for reference. The 
j Fourth (or concluding) section, B is of a more special 
i and technical character, and has been composed 
! almost entirely for the use of practical operators, 
j including those who have not had the advantage of 
chemical instruction : it contains a variety of tech- 
nical points of instruction necessary for the successful 
S prosecution of the art, — information which could not 
be so conveniently classed or supplied in the preceding 
sections. This part also includes a list of all the 
books published on the subject, and an extensive and 
almost complete list of the English Patents (nearly 
300 in number) relating to electro-deposition, taken 
out from the earliest period of the art, until the present 
time. 

I have endeavoured not only to make the book a 
treatise on the practical art of Electro-metallurgy, but 
also to include an outline of the science of electro- 
chemistry, upon which that art is based ; and I have 
also spared no trouble in order to make it as 
perfect as I could ; the most complete portions are 
those which treat of the common methods of silvering, 
gilding, moulding ; the deposition of copper, nickel, 
brass, iron, and tin ; the special details of the art ; 
and the accounts of such experiments and processes 
with the less common metals, as scientific investiga- 
tors and practical inventors, may be likely to further 
examine, or practically apply. 



x Introduction. 

Numerous experiments of my own on the subject, 1 
(many of them, through want of previous opportunity, 
being now for the first time published), are scattered 
through the first part of the Practical section of the 
book ; a few of them being made to fill up missing 
links, whilst the book was in progress. I had hoped 
also to have made others in a similar way, for the 1 
purpose of settling some debateable questions still 
remaining; for instance, to determine whether alumi- 1 
nium is, or is not, capable of being deposited from an 
aqueous solution ; but, owing to the deficiency of en- 
couragement of original scientific research in this 
country, I have been deterred from so doing. 

I beg to express my indebtedness to Mr. E. W. 
BALL, and to my colleague, Mr. A. BRUCE, F.C.S., for j 
the assistance they have kindly rendered me in cor- 1 
recting the proof-sheets. 

GEORGE GORE. 

Birmingham, 1877. 



CONTENTS. 



HISTORICAL SKETCH. 

PAGE 

■Earliest known facts of Electro-metallurgy . . . . i 

Volta's discovery of Chemical Electricity, 1799 ... 2 

Decomposition of Water by Nicholson and Carlisle, 1800 

Electrolytic transfer of Acids and Alkalies. Hisinger and Berzelius, 
1803 

Electro-deposition of Metals. Cruikshank, 1804 

Electro-gilding by a separate Current. Brugnatelli, 1805 • 

Electro-deposition of the Alkali-metals. H. Davy, 1807 

Thermo-electricity. Seebeck. 18 12 

Electro-chromy. Nobili, 1826 . ... 

Magneto-electricity. Faraday, 1831 .... 

Definite Electro-chemical Action. Faraday, 1834 

Copying Surfaces in Copper. De la Rue, 1836 

,, Jacobi, Spencer, Jordan, 1839 . 

Mr. Jordan's Paper on Electrotype ..... 

Mr. Spencer's Paper on Electrotype .... 

The single-cell apparatus ...... 

Gilding by Simple Immersion ; Elkington's Process, 1838 
,, contact with zinc ,, ,, ,, 

First employment of Alkaline Cyanides. Dr. Wright, De Ruolz, 1840 21 

Rendering Surfaces conducting by means of Blacklead. Mr. Murray 23 

Deposition by means of a separate Battery-current. Mr. Mason 

Mr. Smee's Experiments in Electro-deposition, 1841 

Electro-deposition of Brass. De Ruolz, 184 1 . 

Deposition by Magneto-electricity. Woolrich, 1842 

Palmer's Process of Glyphography, 1842 
j Application of Thermo-electricity to Plating, 1843 . 
j Discovery of Bright Silver deposition. Milward, 1847 



2 3 



Subsequent advances in the Subject. .... 27 



Xll 



Contents. 



THEORETICAL DIVISION. 



PRINCIPLES AND LAWS UPON WHICH THE ART IS BASED. 



Electrical principles of Electro-metallurgy 

Conduction and Insulation . . . , 

Series of Conductors and Insulators 

Relative Conducting and Insulating Powers of Substances 

Of Solids, Liquids, and Gases 
Effects of Purity and Temperature of Substances on their con 
ductivity ...... 

Heat generated by Conduction-resistance . 
Electro-chemical Action. 

Chief Conditions of Electro-chemical Action . 

Nature of Electro-chemical Action. 

Nomenclature of ditto . 

Usual Phenomena of Electrolysis .... 

Decomposability of different Electrolytes 

Direction of Electrolysis ..... 

Circumstances affecting the Quality of Electro deposits 

Influence of Composition of the Electrolyte . 

Influence of Density of the Current 

Formation of Metallic Crystals 
Circumstances affecting the Quantity of the Deposit . 

Relation of Chemical value of Atoms to Electrolysis . 

Table of Monads, Dyads, Triads, Tetrads, and Hexads 

Equivalency of Electro-chemical Action 

Symbols and Atomic-weights of Elementary Substances 

Definite Electro-chemical Action . . 

Theory of Electrolysis .... 
Secondary Effects of Electrolysis .... 
Alloy of Deposits with the Cathode, and with each other 

Purity of Electro-deposited Metals 
Electrolysis of Mixed Liquids . 

Electro-deposition of Alloys . 
Polarisation of Electrodes 
Formation of Peroxides upon Anodes 
Movements of Liquids during Electrolysis 
Magneto-electric Action ..... 

Fundamental fact of magneto-electric action . 
Thermo-electric Action ..... 
Tables of Thermo-electric capacities of substances 
Chemical Principles of Electro-metallurgy 
Chemico-electric Relations of Substances 



Contents. xiii 

Chemical Principles of Electro-metallurgy — continued 
Chemico-electric Series .... 
Electric relations of Metals in Liquids . 

i. By Immersion of two Metals in one Liquid 

In Acids, Alkalies, Salts, and Fused Substances 

2. By Immersion of one Metal in two Liquids 

3. By Immersion of two Metals in two Liquids . 
Voltaic-currents ..... 
Electro-motive Force ..... 
Potential, and Tension .... 
Current, and Strength of Current 

Resistance ; Internal and External. Intensity of Current 
Measurement of Current .... 

Relative quantities of Electricity produced by different Metals 
Relations of quantity of Current to Electrolysis 



PRACTICAL DIVISION. 

SECTION A. 

General Methods of Electro-Deposition .... 

1. By one Metal in one Liquid, or ' Simple Immersion Process 1 

Examples of ditto 
Observations upon them 

2. By two Metals in one Liquid ; or ' Simple Contact Process ' 

Examples of ditto ...... 

Observations upon them .... 

3. By one Metal in two Liquids .... 

Examples of ditto ..... 

Observations upon them ..... 

4. By two Metals in two Liquids ; or ' Single-cell Process ' 

Examples of ditto ...... 

Observations upon them .... 

5. By a Separate Current ; or ' Battery- Process ' 

Compound depositing Vessels 
Practical Points to be Observed ..... 

Methods of forming a Depositing Solution 
Method of using a Depositing Liquid .... 92 

DEPOSITION OF INDIVIDUAL SUBSTANCES. 

Class I. Gaseous Me tats. 

1. Deposition of Hydrogen ..... 94 

,, ,, by Simple Immersion Process . 94 

,, ,, by Separate Current ,, . 95 

Absorption of Hydrogen by deposited Metals . 96 



XIV 



Contents. 



Deposition of Individual Substances — continued 

Class II. Electronegative or Brittle Metals, 

2. Deposition of Arsenic .... 

,, ,, by Simple Immersion Process . 

,, ,, by Contact with another Metal 

by Separate Current Process 

3. Deposition of Tellurium ' . 

4. Deposition of Antimony, Crystalline and Amorphous . 

,, ,, by Simple Immersion Process 

,, ,, by Separate Current 

,, explosive Antimony . 

5. Deposition of Bismuth ..... 

,, ,, by Simple Immersion Process 

,, „ by Separate Current „ 

Class III. Noble Metals. 

6. Deposition of Osmium .... 

7. Deposition of Ruthenium 

8. Deposition of Rhodium 

9. Deposition of Iridium . 

10. Deposition of Palladium 

Electrolysis of Anhydrous Hydrofluoric acid 

11. Deposition of Platinum 

,, by Simple Immersion Process 
,, by Separate Current ,, 

12. Deposition of Gold 

Preparation of Salts of Gold 

Electrolysis of Fluorides with a gold anode 

Solutions for Electro-gilding 

Gilding by Simple Immersion Process 
,, ,, Contact with Zinc . 
Gold Solutions for Separate Current Process 

Gilding Solution of M. de Ruolz and others . 
Making Gilding Solutions by Battery Process 
Cold Solutions for gilding by Separate Current Process 
Hot 

Coloured Gilding ..... 
Necessity of free Cyanide .... 
Management of Gilding Solutions . 
Gilding Base Metals ..... 
Gilding the insides of Vessels 
Ungilding articles of Silver and Iron . 
Recovery of Gold from Wash-water 

, ,, Cyanide Solutions 

Recovering Gold or Silver, by M. Bolley . 



Contents. 



xv 



Deposition of Individual Substances — continued 

13. Deposition of Silver ...... 

Preparation of Salts of Silver .... 

Chemical characters of Cyanide of Silver . 
Electrolysis of Salts of Silver .... 

Deposition of Silver by Simple Immersion Process 
Silvering by Simple Immersion Process 

,, ,, Contact with Zinc .... 

Solutions for Silvering by means of a separate Current 

Making Cyanide of Silver Solution by Chemical Means 

How to Electro-plate over soft solder 

Making Cyanide of Silver Solution by the Battery Method 

Condensed outline of the French Silver-plating Process 

Deposition of Bright Silver 

Vats for containing Silver Solutions . 

Quality of Electro-deposited Silver 

Management of Silver-plating Liquids 

Rapidity of Deposition of Silver . 

Thickness of Deposited Silver 

Ornamenting Silver-plated Articles 

Dead Silver, Oxidised Silver, Nielled Silver . 

Cleaning articles of Silver .... 

'Stripping' Plated Articles .... 

Analysis of Cyanide of Silver plating Solution 
Recovery of Silver and Gold from Residuary Liquids 
Extraction of Silver by the Wet Method . 

Dry 
Recovery of Gold by the Wet Method 

Dry „ 
Testing the Purity of Silver 
14. Deposition of Mercury ..... 

Ordinary Salts of Mercury 

Deposition of Mercury by Simple Immersion Process 

Electrolysis of Salts of Mercury 

Electrolytic vibrations and sounds 



PACK 
146 

148 
149 
151 

152 

155 

T 55 
156 
164 
165 
166 
167 
169 
171 
172 
178 
178 
180 
180 
182 

183 
184 
187 
191 
192 
192 

193 
194 

195 
195 
196 
196 
197 



Class IV. Base Metals. 



Deposition of Copper .... 
Common Salts of Copper .... 
Electrical relations of Copper . 
Deposition of Copper by Simple Immersion Process 
Electrolysis of Salts of Copper 
Applications of Electro-deposition of Copper 
Coppering Articles by Simple Immersion Process 



198 
198 
199 
199 
200 
202 
202 



XVI 



Contents. 



Deposition of Individual Substances — continued page 

Separation of Copper from Cupriferous Liquids . . 203 

Deposition of Copper by contact with another Metal . 204 

,, ,, ,, Single-cell Process . . 205 

Coppering Iron Cylinders for Calico-printing . . 205 

Deposition of Copper by the Separate Current Process . 206 

Depositing Copper upon Metals generally . . . 206 

,, ,, Zinc, Iron, etc. . . . 207 

Management of Coppering Liquids .... 209 

Rapidity and cost of Electro-depositing Copper . . 210 

Composition of the Dirt upon Copper Anodes . . 210 

Refining crude Copper by Electrolysis . . . 212 

Estimation of Copper in Solutions by Electrolysis . . 213 

Preventing Adhesion of Deposited Copper to Surfaces . 214 

Copying Engraved Metal Plates in Copper . . .214 

,, Daguerreotype pictures ,, . . 215 
Coating Cloth with Copper ..... 216 

Depositing Copper upon Non-metallic Surfaces . . 216 

Rendering Non-metallic Surfaces Conductive . .217 

Coppering Lamp-posts, Ornamental Ironwork, etc. . 221 

Coppering Fruit, Flowers, Insects, etc. . . . 221 

Coating Plaster models and Clay figures with Copper . 222 

Copying Wood engravings in Copper . . . 222 

,, set-up Type ,, . . . 223 

Moulding and Copying Coins, etc., in Copper . . 224 

Elastic Moulding Composition .... 227 

Copying Busts, Statuettes, Statues, etc. . . . 227 

Glyphography . . . . . .231 

Etching Copper Plates by Electrolysis . . -231 

Depositing Copper upon Glass, Porcelain, etc. . . 232 

16. Deposition of Nickel . . ' . . . 232 

Ordinary Salts of Nickel ..... 232 
Electrolysis of Nickel Solutions .... 232 

Deposition of Nickel by the Simple Immersion Process . 235 

,, ,, by Contact with another Metal . 236 

by Separate Current Process . 236 
Management of Nickel Solutions .... 238 

Properties and uses of Electro-deposited Nickel . . 240 

Estimation of Nickel by means of Electrolysis . . 240 

17. Deposition of Cobalt ..... 241 

Ordinary, Salts of Cobalt . . . . .241 

Electrolysis of Cobalt Solutions .... 242 

Deposition of Cobalt by Contact with another Metal . 242 

,, ,, ,, Separate Current Process . 242 

18. Deposition of Iron ...... 243 

Common Salts of Iron ..... 243 



Contents. 



xvn 



23- 



24. 



Deposition of Individual Substances — continued. 

Deposition of Iron by Simple Immersion Process 
Electrolysis of Salts of Iron 
Coating Engraved Copper Plates with Iron . 
Management of Solutions for Depositing Iron 
Properties and uses of Electro-deposited Iron 

19. Deposition of Manganese .... 

Common Salts of Manganese .... 
Deposition of Manganese by Simple Immersion Process 
Electrolysis of Salts of Manganese 

20. Deposition of Chromium .... 

Common Salts of Chromium .... 
Deposition of Chromium by Simple Immersion Process 
, , , , by a Separate Current 

21. Uranium ...... 

Ordinary Salts of , , 
Electrolysis of Uranium Solutions 

22. Tungsten ...... 

Electrolysis of Salts of Tungsten . 
Molybdenum ...... 

Ordinary Salts of „ . 

Electrolysis of Molybdic Acid .... 
Vanadium ...... 

Electrolysis of Vanadic Acid .... 

25. Deposition of Lead ..... 
Common Salts of Lead .... 
Deposition of Lead by Simple Immersion Process 

,, ,, „ Contact with a Second Metal 

,, ,, ,, a Separate Current 

,, of Peroxide of Lead upon Anodes 

Electro-chromy ..... 

26. Deposition of Thallium ..... 
Electrolysis of Salts of Thallium . 

27. Deposition of Indium ..... 

28. Deposition of Tin ..... 
Common Salts of Tin ..... 
Electrical relations of Tin and Iron 
Depositing Tin by Simple Immersion Process 

Contact with a Second Metal . 
Electrolysis of Salts of Tin .... 
Deposition of Tin by Separate Current Process . 
,, ,, Alloys of Tin and Copper 

29. Deposition of Cadmium .... 
Common Salts of Cadmium .... 
Deposition of Cadmium by contact with another Metal 

,, ,, ,, Separate Current Process 



XV111 



Contents. 



Deposition of Individual Substances — continued 

30. Deposition of Zinc .... 

Common Salts of Zinc .... 
Deposition of Zinc by Simple Immersion Process 
,, Contact with another Metal 
,, ,, ,, Separate Current Process 

Estimation of Zinc by means of Electrolysis 
Deposition of Alloys of Zinc and Copper 
Solutions for Electro-depositing Brass 
Electro-deposition of German-silver . 
Separation of Copper and Zinc by Electrolysis 



Class V. Earth and Alkaline Earth Metals, 

31. Deposition of Magnesium 
Common Salts of Magnesium 
Electrolysis of Magnesium Solutions 

32. Deposition of Cerium. Lanthanium, and Didymium 

33. Deposition of Gallium . 

34. Deposition of Aluminium 
Electrolysis of Salts of Aluminium 

35. Deposition of Glucinium 

36. Deposition of Calcium 
Common Salts of Calcium . 
Electrolysis of Salts of Calcium 

37. Deposition of Strontium 
Electrolysis of Salts of Strontium 

38. Deposition of Barium 
Electrolysis of Salts of Barium . 



Class VI. Alkali Metals 



39. Deposition of Lithium . 
Electrolysis of Salts of Lithium 

40. Deposition of Sodium . 
Ordinary Salts of Sodium 
Electrolysis of Salts of Sodium . 

41. Deposition of Potassium 
Ordinary Salts of Potassium 
Electrolysis of Salts of Potassium . 
Electrolysis of Fused Potassic Fluoride 

42. Deposition of Rubidium and Caesium 

43. ,, ,, Ammonium 
Electrolysis of Salts of Ammonium „ 



Contents. 



xix 



Deposition of Individual Substances— continued. 

Class VII. Metalloids. 
44. Deposition of Titanium . 



45- 


, Silicon 


46. 


, Boron 


47- 


, Carbon 


48. 


, Phosphorus 


49- 


, Selenium 


50. 


, Sulphur . 


5 1 - 


Iodine 


52. 


Bromine . 


53- 


, Chlorine 


54- 


, Fluorine . 


55- 


Oxygen 


56. 


, Nitrogen . 



SECTION B. 
SPECIAL TECHNICAL SECTION. 

General Workshop Arrangements . 

Vats for Solutions 

Cleaning Articles for receiving a deposit 

'Stopping off' to prevent Deposition . 

■ Qi.icking ' the surfaces of Articles . 

'Wireing' Articles 

Voltaic Batteries .... 

Wollaston's 

Smee's ..... 

Daniell's .... 

Bunsen's ..... 

Grove's .... 

Relative strength of different Batteries 

„ advantages 
Liquids for Exciting Batteries 
Amalgamating zinc plates and rods 
Selection of Zinc for Batteries 
Outer Cells for Batteries 
Selection of Porous Cells for Batteries 
Screws for Binding and connecting Wires, &c 
Management of Batteries 
Regulation of Electric-power 
Selection of Depositing Processes . 
' Pyro-plating ' . 
Selection of Depositing Liquids . . 



xx Contents. 



PAGE 



Testing a Depositing Liquid ...... 341 

Practical Arrangement of Depositing Solutions . . . 341 

Proper positions of Articles and Dissolving Plates in the Vats . . 343 

Regulation of Deposit ...... 344 

Magneto-electric Machines ...... 347 

Thermo-electric Piles . . . . . . 351' 

SPECIAL INFORMATION RESPECTING SUBSTANCES, ETC., USED IN 
THE ART. 

Water, Acids, Salts, Alkalies, Blacklead, &c. . . 354 

Preparation of Caustic-potash . ..... 360 

Making Cyanide of Potassium . . . . .361 

Testing ,, ,, ..... 363 

Poisons and their Antidotes, dfc. ..... 365 

List of Books on Electro-deposition ..... 369 

Patents ,,,,..... 371 

Tables of Useful Numerical Data . . . . . 385 

Nomenclature of Electrical Units ..... 387 1 

INDEX .389 



THE 

ART OF ELECTRO-METALLURGY. 

HISTORICAL SKETCH OF ELECTRO-METALLURGY. 

The earliest known facts respecting the electro-deposition 
of metals were those in which one metal, by being dipped 
into a solution of another, became coated with the latter 
metal. For instance, iron or steel, when dipped into a solu- 
tion of blue vitriol, became covered with a coating of copper ; 
copper, dipped into a solution of mercury, became amalga- 
mated ; zinc, immersed in a solution of lead, formed a tree 
of lead, and in one of silver produced the arbor Diana. 
These and other similar facts of a chemical nature were 
known long before the discovery of voltaic electricity. 
Gilding and silvering on metals had been known for many 
ages ; gilded statues and bronzes have been found in the 
tombs of the ancient Egyptians. Both Pliny and Vitruvius 
speak of processes of gilding and silvering ; but these early 
processes appear to have been effected by means of amal- 
gams of mercury, and not by electro-chemical methods. 
Zosimus, however, speaks of the deposition of bright metal- 
lic copper from its solution by means of iron. Paracelsus 
also and Bernard de Palissy, a thousand years later, were 
acquainted with, and describe, the means of coating copper 

B 



2 The A rt of Electro- Metallurgy. 

and iron with silver by simple immersion in a solution of I 
silver. 

One of the earliest recorded facts in connection with 
voltaic electrolysis is that observed by Sulzer, who in the 
year 1752 remarked : 'If you join two pieces of lead and 
silver, so that they shall be upon the same plane, and then 
lay them upon the tongue, you will notice a certain taste re- 
sembling that of green-vitriol, while each piece apart produces 
no such sensation ' (' Histoire de l'Academie des Sciences et 
Belles-Lettres de Berlin'). The earliest known fact of elec- 
trolysis by separate electric discharge appears to be that of 
Paetz and Van Troostwik, who in the year 1790 decom- 
posed water into its two constituent gases, bypassing electric 
sparks through it by means of very fine gold wires (De la 
Rive's ' Treatise on Electricity/ vol. ii., p. 443). 

But all these were empirical, stagnant, and comparatively . 
unfruitful facts ; no great progress resulted from them because 
they were not generalised upon, and were not recognised as 
instances of any great law or principle. Electrolysis did not 
start into active and real progress until after Volta made his 
great discovery of chemical electricity in the year 1 7 99. About 
that time he produced his crown of cups, which was the 
first arrangement by means of which a current of voltaic 
electricity could be produced for any continued length of time. 

Cruickshank soon afterwards devised his well-known 
trough battery, in which zinc and copper plates were fixed ! ); 
in vertical grooves, so as to form a more powerful and com- 
pact arrangement (Highton's ' Electric Telegraph/ pp. 13, 14, 
and 29). 

Nicholson and Carlisle, on May 2, 1800, first decomposed 
water by means of a voltaic current (Highton's ' Electric Te- 
legraph/ pp. 27 and 29). \ 

Dr. Henry, of Manchester, also about the same year, de- 
composed nitric and sulphuric acids, and resolved ammonia 
into its constituent gases by similar means (' Encyclopedia 
Metropolitana/ vol. iv., pp. 22 t and 611). 



Early Facts of Electrolysis. 3 

In the year 1801 Wollaston remarked that 'if a piece of 

silver, in connection with a more positive metal, be put into 

1 a solution of copper, the silver is coated over with copper, 

i which coating will stand the operation of burnishing' (' Philo- 

! sophical Transactions of the Royal Society/ 1801). 

In the same year Gerboin first noticed the movements 
I of mercury in a conducting liquid when a voltaic current was 
I passed through the liquid metal; we now know that those 
] movements were due to electrolysis (De la Rive's ' Treatise 
I on Electricity,' vol. ii., p. 433). Hisinger and Berzelius also, 
\ in 1803, found by means of many experiments that, under 
j the influence of a voltaic current, the elements of water and 
\ of neutral salts were transferred to the respective poles of the 
j battery (' Encyclopedia Metropolitana,' vol. iv., pp. 221, 222). 
About the same time Cruickshank passed a voltaic current, 
by means of silver wires, through solutions of acetate of lead, 
sulphate of copper, nitrate of silver, and several other salts, 
and found that the metals attached themselves to the wire 
connected with the zinc-end of the battery ; and stated that 
the metals were 'revived' so completely as to suggest tohirn 
the analysis of minerals by means of the voltaic current 
(Wilkinson's 'Elements of Galvanism,' vol. ii., 1804, p. 54). 
The first result of a decidedly practical form in electro - 
gilding was that of Brugnatelli, who, in the year 1805, gilded 
two silver medals by making them the negative pole in a 
newly-made and well-saturated solution of ammoniuret of 
gold (' Philosophical Magazine,' 1805). He also electro- 
deposited bright metallic silver upon platinum, and ob- 
served that when the current entered the liquid by means 
of a pole of copper or zinc, those metals were dissolved 
and then deposited upon the negative pole (see his ' Annals 
of Chemistry'). One of the greatest discoveries in the 
subject, however, was that of Sir Humphry Davy, made on 
October 6, 1807. ^ e passed a powerful electric cur- 
j rent, from a battery composed of 274 cells, through a frag- 
ment of moistened potash, and deposited the metal potassium 



4 The A rt of Electro-Metallurgy. 

itself upon the negative platinum wire. Seebeck, of Berlin, in 
the year 1822 discovered thermo-electricity by observing that, 
when the soldered junction of two different metals (bismuth 
and copper) was heated, an electric current was produced. 
In 1824 Sir H. Davy attempted to protect the copper sheath- 
ing of ships by means of strips of zinc attached to it. Nobili, 
in the year 1826, discovered that when a current of voltaic 
electricity was passed into a solution of acetate of lead by 
means of a plate of platinum, and out of it by means of a pla- 
tinum wire, rings of beautiful colours, caused by the forma- 
tion of thin films of peroxide of lead, appeared on the 
platinum plate ; this effect was named ' metallo-chromy.' 

Magneto-electricity was discovered by Faraday. In the 
year 1 83 1 he produced a spark by pulling a keeper (covered 
with a coil of insulated wire) from the poles of a magnet ; he 
also obtained a magneto electric current by rotating a copper 
plate between the poles of a magnet, and by sliding a coil of 
insulated copper wire upon a steel-bar magnet. In 1834 he 
made the important discovery, that when a voltaic current 
was passed through different salts in solution or in a state of 
fusion, the amount of salt decomposed by the current was in 
direct proportion to the quantity of electricity ; and that the 
quantities of substances dissolved and set free in electrolysis 
were in definite proportions by weight, and that those pro- 
portions were identical with the ordinary chemical equiva- 
lents of the substances, and thus established the important 
law of definite electro -chemical action. He also proved that 
the quantity of electricity from a voltaic battery depends 
upon the size of the immersed portion of the plates, and that 
the intensity of the current depends upon the number of al- 
ternate pairs of metals ; and used a voltameter to ascertain 
the strength of the current. 

In 1836 Mr. De la Rue devised a peculiar form of 
Daniell's battery, and observed that - the copper plate is also 
covered with a coating of metallic copper, which is continu- 
ally being deposited ; an d so perfect is the sheet of copper 



Jordan's Experiments. 5 

- thus formed that, being stripped off, it has the counterpart 
|| of every scratch of the plate on which it is deposited ' 
I ('Philosophical Magazine,' 1836). 

In 1837 Dr. Golding Bird decomposed, by means of a 
i voltaic current, solutions of the chlorides of sodium, potas- 
' sium, and ammonium, and deposited their respective metals 
I on a negative pole of mercury, and thus obtained their amal- 
|! gams ('Philosophical Transactions of the Royal Society/ 1837, 

j P- 37)- 

Several persons now made experiments upon the electro- 

1 deposition of metals at about the same time, and brought 
|| electro-metallurgy into prominent notice. Professor Jacobi, 
j of St. Petersburg, published his galvano-plastic process, ' a 
1 method of converting any line, however fine, engraved on 
; copper, into a relief by galvanic process, applicable to cop- 
I per-plate engravings, medals, stereotype plates, ornaments, 
j and to making calico-printing blocks and patterns for paper- 
j hangings' ('Athenaeum,' May 4, 1839). Mr. T. Spencer, of 
' Liverpool, also on May 8, 1839, gave notice to read a paper 
' on the ' Electrotype Process ' to the Liverpool Polytechnic 
Society, but the paper was not read until September 13 in the 
same year. 

Meanwhile, Mr. C. J. Jordan, on May 22, 1839, sent a 
letter to the 'London Mechanics' Magazine,' which was pub- 
lished on June 8, 1839. After stating that his experiments 
were made ' about the commencement of last summer, with 
a view of obtaining impressions from engraved copper 
plates/ it proceeds as follows : 

1 It is well known to experimentalists on the chemical 
action of voltaic electricity that solutions of several metallic 
salts are decomposed by its agency, and the metal procured 
in a free state. Such results are very conspicuous with cop- 
per salts, which metal may be obtained from its sulphate 
(blue vitriol) by simply immersing the poles of a galvanic 
battery in its solution, the positive wire becoming gradually 
coated with copper. This phenomenon of metallic reduction 



6 The Art of Electrc-Metallurgy. 

is an essential feature in the action of sustaining batteries, 
the effect, in this case, taking place on more extensive sur- f 
faces. But the form of voltaic apparatus which exhibits this 
result in the most interesting manner, and relates more im- 
mediately to the subject of the present communication, may- 
be thus described : It consists of a glass tube, closed at one 
extremity with a plug of plaster-of- Paris, and nearly filled 
with a solution of sulphate of copper ; this tube and its con- 
tents are immersed in a solution of common salt. A plate 
of copper is placed in the first solution, and is connected by 
means of a wire and solder with a zinc plate, which dips 
into the latter. A slow electric action is thus established 
through the pores of the plaster, which it is not necessary to 
mention here ; the result of which is the precipitation of 
minutely crystallised copper on the plate of that metal, in a 
state of greater or less malleability, according to the slowness 
or rapidity with which it is deposited. In some experiments 
of this nature, on removing the copper thus formed I re- 
marked that the surface in contact with the plate equalled 
the latter in smoothness and polish, and mentioned this fact 
to some individuals of my acquaintance. It occurred to me, 
therefore, that if the surface of the plate was engraved an 
impression might be obtained. This was found to be the 
case, for, on detaching the precipitated metal, the most deli- 
cate and superficial marking, from the fine particles of pow- 
der used in polishing to the deeper touches of a needle or 
graver, exhibited their corresponding impressions in relief 
with great fidelity. It is, therefore, evident that this princi- 
ple will admit of improvement, and that casts and moulds 
may be obtained from any form of copper. 

' This rendered it probable that impressions may be ob- 
tained from those other metals having an electro-negative 
relation to the zinc plate of the battery. With this view, 
a common printing type was substituted for the copper-plate, 
and treated in the same manner. This also was successful ; 
the reduced copper coated that portion of the type immersed 



Spencer s Experiments, y 

in the solution. This, when removed, was found to be a 
perfect matrix, and might be employed for the purpose of 
casting when time is not an object. 

' It appears, therefore, that this discovery may be turned 
to practical account. It may be taken advantage of in pro- 
curing casts from various metals, as above alluded to ; for 
instance, a copper die may be formed from a cast of a coin 
or medal, in silver, type metal, or lead, &c, which may be 
employed for striking impressions in soft metals. Casts 
may probably be obtained from a plaster surface surrounding 
a plate of copper ; tubes or any small vessel may also be 
made by precipitating the metal around a wire, or any kind 
of surface, to form the interior, which may be removed me- 
chanically, by the aid of an acid solvent, or by heat. 

1 C. J. Jordan. 

'May 22, 1839.' 

Mr. Spencer in his paper, after making some preliminary 
remarks, states : — 'In the latter part of September 1837 I 
was induced to make some electro-chemical experiments 
with single pairs of plates, consisting of small pieces of zinc 
and equal-sized pieces of copper, connected together with 
wires of the latter metal. It was intended that the action 
should be slow ; the fluids in which the metallic electrodes 
were immersed were in consequence separated by thin discs 
of plaster-of-Paris. In one cell thus formed was placed 
sulphate of copper in solution, in the other a weak solution 
of common salt. I need scarcely add that the copper 
electrode was placed in the cupreous solution, the other 
being in that of the salt. I mention these experiments 
briefly ; not because they are directly connected with what 
I shall have to lay before the Society, but because, by a 
portion of their results, I was induced to come to the con- 
clusions I have done in the following paper. I was desirous 
that no action should take place on the wires by which the 
electrodes were held together; and to obtain this object I 



8 The A rt of Electro-Metallurgy. 

varnished them with sealing-wax varnish, but in one instance 
I dropped a portion on the copper electrode that was 
attached. I thought nothing of this circumstance at the 
moment, but put the experiment inaction. 

' This operation was conducted in a glass vessel ; I had 
consequently an opportunity of occasionally examining its 
progress from the exterior. After the lapse of a few days, 
metallic crystals had covered the copper electrode — with the 
exception of that portion which had been spotted with the 
drops of varnish. I at once saw that I had it in my power 
to guide the metallic deposition in any shape or form I chose, 
by a corresponding application of varnish or other non- 
metallic substance. 

' I had been aware of what everyone who uses a sustain- 
ing galvanic battery with sulphate of copper must know, that 
the copper plates acquire a coating of copper from the action 
of the battery ; but I had never thought of applying it to a 
useful purpose, except to multiply the plates of a species of 
battery, which I did in 1836. My present attempt was with 
a piece of thin copper plate having about four inches of 
superficies, with an equal-sized piece of zinc, connected as 
before by a piece of copper wire. I gave the copper a coat- 
ing of soft cement, consisting of bees'-wax, rosin, and a red 
earth. It was compounded in the way recommended by 
Dr. Faraday, in his work on Chemical Manipulation, but 
with a larger proportion of wax. The plate received its 
coating while hot. When it was cold, I scratched the initials 
of my name rudely on the plate, taking special care that the 
cement was quite removed from the scratches, that the 
copper might be thoroughly exposed. This was put in action 
in a cylindrical glass vessel, about half filled with a saturated 
solution of sulphate of copper. I then took a common gas 
glass, similar to that used to envelope an argand burner, and 
filled one end of it with plaster-of-Paris acting as a partition 
to separate the fluids, but at the same time being sufficiently 



Spencer's Experiments. 9 

porous to allow the electro-chemical action to permeate its 
substance. 

'I now bent the wire in such a manner that the zinc end 

of the arrangement should be in the saline solution, while 

J the copper end, when in its place, should be in the cupreous 

\ solution. The gas glass, with the wire, was then placed in 

I the vessel containing the sulphate of copper. 

' It was then suffered to remain at rest, when in a few 
j hours I perceived that action had commenced, and that the 
j portion of the copper rendered bare by the scratches had 
i become gradually coated with pure, bright deposited metal, 
whilst all the surrounding portions were not at all acted on, 
I now saw my former observations realised ; but whether 
the deposition so formed would retain its hold on the plate, 
and whether it would be of sufficient solidity or strength to 
bear the working if applied to a useful purpose, became 
questions which I now determined to solve by experiment. 
It also became a question, should I be successful in these 
two points, whether I should be able to produce lines suffi- 
ciently in relief to print from. This latter appeared to 
depend entirely on the nature of the cement or etching- 
ground I might use. 

' This I endeavoured to solve at once ; and, I may state, 
it appeared at the time to be the main difficulty, as my im- 
pression then was, that little less than one-eighth of an inch 
would be requisite to print from. 

' I now procured a piece of copper, and gave it a coating 
of a modification of the cement I have already mentioned, 
and, having covered it to about one-eighth of an inch in 
thickness, I took a steel print and endeavoured to draw lines 
in the form of network, that should entirely penetrate the 
cement, and leave the surface of the copper exposed. But 
in this I experienced much difficulty from the thickness I 
deemed it necessary to use, more especially when I came to 
draw the cross lines of the network. The cement being 
soft, the lines were pushed, as it were, into each other, and 



I o The A rt of Electro-Metallurgy. 

when it was made of harder texture, the intervening squares |i 
of the network chipped off the surface of the metallic plate. | 
However, those that remained perfect I put in action as 
before. 

' In the progress of this experiment I discovered that the 
solidity of the metallic deposition depended entirely on the 
weakness or intensity of the electro-chemical action, which I 
knew I had in my power to regulate at pleasure, by the 
thickness of the intervening wall of plaster-of- Paris, and by 
the coarseness or fineness of the material. I made three 
similar experiments, altering the texture and thickness of the 
plaster each time, by which I ascertained that if the parti- 
tions were thin and coarse, the metallic depositions proceeded 
with great rapidity, but the crystals were pliable and easily 
separated ; on the other hand, if I made them thicker, and 
of a little finer material, the action was slower, but the me- 
tallic deposition was as solid and ductile as copper formed 
by the usual methods ; indeed, when the action was exceed- 
ingly slow, I have had a metallic deposition apparently 
much harder than common sheet-copper, but more brittle. 

1 There was one most important, and to me discouraging, 
circumstance attending these experiments, which was, that 
when I heated the plates to get off the covering of cement, 
the meshes of copper network occasionally came off with 
it. I at one time imagined this difficulty insuperable, as 
it appeared that I had cleared the cement entirely from 
the surface of the copper that I meant to have exposed; and 
I concluded that there must be differences in the molecular 
arrangement of copper prepared by heat and that prepared 
by voltaic action which prevented their chemical combina- 
tion. However, I determined, should this prove so, to 
turn it to account in another manner, which I shall 
relate in the second portion of the paper. 

' 1 now occupied myself for a considerable period in 
making experiments on this latter section of the subject. 

' In one of them I found, on examination, that a portion 



Spencer's Experiments. 1 1 

of the copper deposition, which I had been forming on the 
surface of a coin, adhered so strongly that I was quite 
unable to get it off; indeed, a chemical combination had 
apparently taken place. This was only on one or two spots 
j on the prominent parts of the coin. I immediately recol- 
• lected that on the day I put the experiment in action I had 
: been using nitric acid for another purpose on the table I 
\ was operating on, and that in all probability the coin might 
| have been laid down where a few drops of the acid had acci- 
' dentally fallen. Bearing this in view, I took a piece of cop- 
| per, coated it with cement, made a few scratches on its surface 
j until the copper appeared, and immersed it for a short time 
j in dilute nitric acid, until I perceived, by an elimination of 
nitrous gas, that the exposed portions were acted upon 
sufficiently to be slightly corroded. I washed the copper in 
water, and put it in action as before described. In forty- 
eight hours I examined it, and found the lines were entirely 
filled with copper. I applied heat, and then spirits of tur- 
pentine, to get off the cement, and, to my satisfaction, I 
found that the voltaic copper had completely combined it- 
self with the sheet in which it was deposited. 

' I then gave a plate a coating of cement to a considerable 
thickness, and sent it to an engraver; but when it was 
returned I found the lines cleared out so as to be wedge- 
shaped, or somewhat in the form of a V, leaving a hair-line of 
the copper exposed at the bottom, and a broad space near 
the surface ; and where the turn of the letters took place the 
top edges of the lines were galled and rendered rugged by 
the action of the graver. This, of course, was an important 
objection, which I have since been able to remedy in some 
degree by an alteration in the shape of the graver, which 
should be made of a shape more resembling a narrow paral- 
lelogram than those m common use : some engravers have 
many of their tools so made. I did not put this plate in 
action, as I saw that the lines, when in relief, would have 
been broad at the top and narrow at the bottom. I took 



1 2 The A rt of Electro-Metallurgy. 

another plate, gave it a coating of the wax, and had it writ- 
ten on with a mere point. I deposited copper on the lines, 
and afterwards had it printed from.* 

' I now considered part of the difficulty removed : the 
principal one yet remaining was to find a cement, or etching- 
ground, the texture of which should be capable of being cut 
to the required depth, without raising what is technically 
called a burr, and at the same time of sufficient toughness 
to adhere to the plate when reduced to a small, isolated 
point, which would necessarily occur in the operation which 
wood-engravers term cross-hatching. 

' I have since learned from practical engravers that much 
less relief is necessary to print from than I had deemed 
indispensable, and that, on becoming more familiar with the 
cutting of the wax-cement, they would be enabled to engrave 
in it with facility and precision. 

' I tried a number of experiments with different combina- 
tions of wax, resins, varnishes, earths, and metallic oxides, 
all with more or less success. One combination that ex- 
ceeded all others in its texture was principally composed of 
bees'-wax, resin, and white-lead. This had nearly every 
requisite, so that I was enabled to polish the surface of the 
plate with it until it was nearly as smooth as a plate of glass. 
With this compound I had two plates, five inches by seven, 
coated over, and portions of maps cut on the cement, which 
I had intended should have been printed off. I applied \ 
the same process to these as to the others, immersing them 
into dilute nitric acid before putting them in action — indeed 
I suffered them to remain about ten minutes in the solution. 
I then put them into the voltaic arrangement. The action 
proceeded slowly and perfectly for a few days, when I re- 
moved them. I applied heat, as usual, to remove the cement, 
but all came away, as in a former instance — the voltaic 
copper peeling off the plate with the greatest facility. I 

* This plate was shown to friends, and also specimens of printing 
from it, in 1838. 



Spencer's Experiments 1 3 

jwas much puzzled at this unexpected result, but, on cleaning 
I the plate, I discovered a delicate trace of lead, exactly cor- 
i responding to the lines drawn on the cement previous to the 
! immersion in the dilute acid. The cause of this failure was 
; at once obvious : the carbonate of lead I had used to com- 
pound the etching- ground had been decomposed by the 
■ dilute nitric acid, and the metallic lead thus reduced had 
;| deposited itself on the exposed portions of the copper plates, 
I preventing the voltaic copper from chemically combining 
: with the sheet of copper. I was now with regret obliged to 
!j give up this compound and to adopt another, consisting of 
j bees'-wax, common resin, and a small portion of plaster-of- 
! Paris. This seems to answer the purpose tolerably, though 
I I have no doubt, by an extended practice, a better may still 
be obtained by a person practically acquainted with the 
1 etching-grounds in use among engravers. 

1 1 now proceed to the second, and, I believe, the most 
satisfactory portion of the subject. Although I have placed 
these experiments last, some of them were made at the 
same time with the others already described, and some of 
them before ; but to render the subject more intelligible I 
have placed them thus. 

' The members of the Society will recollect that, on the 
first evening it met, I read a paper on the " Production of 
Metallic Veins in the Crust of the Earth," and that, among 
other specimens of cupreous crystallization which I produced 
on that occasion, I exhibited two coins, — one wholly covered 
with metallic crystals, the other on one side only. It was 
used under the following circumstances : when about to 
make the experiment, I had not a slip of copper at hand to 
form the negative end of my arrangement, and, as a good 
substitute, I took a penny and fastened it to one end of the 
wire and put it, in connection with a piece of zinc, in the 
apparatus already described. 

Voltaic action took place, and the copper coin became 
covered with a deposition of copper in a crystalline form. 



1 4 The A rt of Electro- Metallurgy. 

But when about to make another experiment, and being de- 
sirous of using the piece of wire used in the first instance, 
I pulled it off the coin to which it was attached. In doing 
this, a piece of the deposited copper came off with it ; on 
examining the under portion of which, I found it contained 
an exact mould of a part of the head and letters of the coin, 
as smooth and sharp in every respect as the original on 
which it was deposited. I was much struck with this at the J 
time, but, on examination, the deposited metal was very 
brittle. This, and the fact that it would require a metallic I 
nucleus to aggregate on, made me apprehensive that its f 
future usefulness would be materially abridged ; but it was 
reserved for future experiment, and in consequence laid aside 
for a time, until my attention was recalled to the subject in 
a subsequent experiment, already detailed, by the drops of 
varnish on a slip of copper. Finding in this instance that 
the deposit would take the direction of any non-conducting 
material, and be, as it were, guided by it, I was induced to 
give the previous branch of the subject a second trial, be- 
cause I had, in the first instance, supposed that the deposi- 
tion would only take place continuously, and not as isolated 
specks of a metallic surface, as I now found it would ; but 
the principal inducement to investigate the subject was the 
fact of finding that the deposited copper had much more f 
tenacity than I at first imagined. 

' Being aware of the apparent natural law which limits 
metallic deposition by voltaic electricity, excepting in the | 
presence of a metallic body, I perceived that the uses of the | 
process would in consequence be extremely limited, except 
in the multiplication of already- engraved plates, as, what- 
ever ornament it might produce, it would only be done by 
adhering to the condition of a metallic mould. 

'I accordingly determined to make an experiment on a 
very prominent copper medal. It was placed in a voltaic 
circuit, as already described, and deposited a surface of 
copper on one of its sides, to about the thickness of a shilling. 



Spencer's Experiments. 1 5 

II then proceeded to get the deposition off. In this I expe- 
rienced some difficulty, but ultimately succeeded. On ex- 
jamination with a lens, every line was as perfect as the coin 
ifrom which it was taken. I was then induced to use the 
I same piece again, and let it remain a much longer time in 
^action, that I might have a thicker and more substantial 
I mould, in order to test fairly the strength of the metal. It 

I was accordingly put again in action, and let remain until it 
had acquired a much thicker coating of the metallic deposi- 
tion ; but on attempting to remove it from the medal I 
found I was unable. It had apparently completely adhered 
to it. 

' I had often practised with some degree of success a 

I method of preventing the oxidation of polished steel, by 
slightly heating it until it would melt fine bees'-wax ; it was 
then wiped apparently completely off, but the pores or sur- 
face of the metal became impregnated with the wax. 

1 1 thought of this method, and applied it to a copper 
coin. 

'I first heated it, applied wax, and then wiped it so com- 

: pletely off, that the sharpness of the coin was not at all in- 
terfered with. I proceeded as before, and deposited a 
thick coating of copper on its surface. Being desirous to 
take it off, I applied the heat of a spirit lamp to the back, 
when a sharp crackling noise took place, and I had the 
satisfaction of perceiving that the coin was completely 
loosened. In short, I had a most complete and perfect 
copper mould of one side of a halfpenny. 

* I have since taken some impressions from the mould 
thus taken, and by adopting the above method with the 

i wax, they are separated with the greatest ease. 

' By this experiment it would appear that the wax impreg- 

I nates the surface of the metal to an inconsiderable depth, 

j and prevents a chemical adhesion from taking place on the 

i two surfaces; and I can only account for the crackling noise 
on separation, by supposing it probable that the molecular 



1 6 The A rt of Electro-Metallurgy. 

arrangement of the voltaic metal is different from that sub- 
jected to percussion, and this difference causes an unequal 
degree of expansibility on the application of heat. 

1 1 now became of opinion that this latter method might 
be applied to engraving much better than the method de- 
scribed in the first portion of this paper. Having found in a 
former experiment that copper in a voltaic circuit deposited 
itself on lead, with as much rapidity as on copper, I took a 
silver coin and put it between two pieces of clean sheet-lead, 
and placed them under a common screw-press. From the 
softness of the lead, I had a complete and sharp mould of 
both sides of the coin, without sustaining injury. I then 
took a piece of copper wire, soldered the lead to one end 
and a piece of zinc to the other, and put them into the 
voltaic arrangement I have already described. I did not in 
this instance wax the mould, as I felt assured that the de- 
posited copper would easily separate from the lead by the 
application of heat, from the different expansibility of the 
two metals. 

* In this result I was not disappointed. When the heat 
of a spirit lamp was applied for a few seconds to the lead 
the copper impression came easily off. So complete do I [ 
think this latter portion of the subject, that I have no hesita- 
tion in asserting \haX facsimiles of any coin or medal, no 
matter of what size, may be readily taken, and as sharp as 
the original. To test further the capabilities of this method 
I took a piece of lead plate, and stamped some letters on its 
surface to a depth sufficient to print from when in relief. I 
deposited the copper on it, and found it came easily off, the 
letters being in relief. 

i Finding from this experiment that the extreme softness 
of the lead allowed it to be impressed on by type-metal, I 
caused a small portion of ornamental letter-press to be set 
up in type, and placing it on a planed piece of sheet-lead, it 
was subjected to the action of a screw-press. 

' After considerable pressure, it was found that a perfectly 



Spencer's Experiments. \j 

sharp mould of the whole had been obtained in the lead. A 
wire was now soldered to it, and it was placed in an 
| apparatus similar in principle, but larger than the one al- 
i ready described. At the end of eight days from this time 
j copper was deposited to one-eighth of an inch in thickness ; 
\ it was subjected to heat, when the two metals began to 
| loosen. The separation was completed by inserting a piece 
: of wedge-shaped wood between them. 

1 1 had now the satisfaction of perceiving that I had ob- 
tained a most perfect specimen of stereotyping in copper, 
which had only to be mounted on a wooden block to be 
ready to print from. 

1 From the successful issue of this experiment, which was 
i mainly due to the susceptibility of the lead, I was induced 
I to attempt to copy a wood engraving by a similar method, 
j provided the wood would bear the requisite pressure. Know- 
ing that wood engravings are executed on the end of the 
block, I had better hopes of succeeding, the wood being less 
likely to sustain injury. 

' I accordingly procured a small block, and placed its 
engraved surface in contact with a piece of sheet-lead, made 
very clean, and subjected it to pressure as in the former in- 
stance. I had now, as before, the gratification of perceiving 
that a perfect mould of the little block had been obtained, 
and no injury done to the original. Several wood engravings 
j and copper plates were subjected to similar treatment, and 
are now in process of being deposited on in the apparatus 
before me. 

' I now come to the third and concluding portion of the 
experiments on this subject, the object being to deposit a 
metallic surface on a model of clay, wood, or other non- 
metallic body, as otherwise I imagined the application of 
this principle would be extremely limited. Many experi- 
ments were made to attain this result, which I shall not 
detail, but content myself with describing those which were 
ultimately most successful. 



18 



The Art of Electro-Metallurgy. 



1 1 procured two models of an ornament — one made of 
clay, and the other of plaster-of- Paris, soaked them for some 
time in linseed-oil, took them out and suffered them to dry. 
I gave them a thin coat of mastic varnish. When the varnish 
was nearly dry, but not thoroughly so, I sprinkled some bronze 
powder on that portion I wished to make a mould of. This 
powder is composed of mercury and sulphur, or it may be 
chemically termed a sulphuret of mercury. There is a sort 
which acts much better, in which is a portion of gold. I 
had, however, a complete metalliferous coating on the sur- 
face of the model, by which I was enabled to deposit a sur- 
face of copper on it by the voltaic method I have already 
described. I have also gilt the surface of a clay model with 
gold leaf, and have been successful in depositing copper on , 
its surface. There is another, and, as I trust it will prove, a 
similar method of attaining this object ; but, as I have not 
sufficiently tested it by experiment, I shall take another op- 
portunity of describing it.' The reading of this paper was 
accompanied by an exhibition of specimens of coins, medals, 
and copper plates, formed by the electrotype process. 

The publication of Mr. Spencer's paper excited general 
attention, and thousands of persons of all classes of society 
at once became fascinated by the new 
art ; and various improvements were f 
made which soon led to its becoming a \ 
definite manufacturing process. 

The apparatus commonly employed 
at this period was what is termed; 
the ' single cell,' and is shown in the | 
annexed figure, in which A is a wide, 
open jar of glass or earthenware, nearly < 
filled with a saturated solution of blue k 
vitriol (sulphate of copper). B is as 
narrow and much taller jar, made of 
porous earthenware, containing dilute sulphuric acid, and 
filled to the same level as the outer vessel. C is a tall rod of 



Fig 




Single-cell Process. 1 9 

cast zinc immersed in the acid, and supported in the centre of 
the jar. D is a coin or medal, suspended in the copper solution, 
\ and attached by means of a copper wire to the rod of zinc ; 
il and E is a perforated copper shelf placed near the top of the 
; liquid, upon which are placed crystals of blue vitriol to sup- 
\ ply copper to the solution as fast as it is extracted by the 
i| depositing process. For the circular vessel A, and round 
j! porous cell B, and cast rod of zinc C, were soon afterwards 
| substituted rectangular-shaped vessels, which are more con- 
'| venient, and a plate of rolled zinc coated with mercury. 

At this period several persons were attempting to make 

|j electro-plating a profitable speculation. Foremost among 

j these were Messrs. G. R. and H. Elkington, who were en- 

I gaged commercially in the year 1838 in coating military and 

; other metal ornaments with gold and silver, by simply im- 

I mersing them in solutions of those metals, particularly a 

j boiling one of carbonate of potash containing dissolved gold. 

They also employed and patented, in conjunction with 

! O. W. Barratt (July 24, 1838), a process for coating articles of 

I copper and brass with zinc, by means of an electric current, 

generated by a piece of zinc attached to the articles by a 

wire, and immersed with them in a boiling and neutral 

solution of chloride of zinc. This was the first patent in 

which a separate metal was employed for electro-plating 

purposes. 

During the year 1840 Mr. John Wright, a surgeon in Bir- 
mingham, and Mr. Alexander Parkes, an experimentalist in the 
employment of Messrs. Elkington, were engaged in electro-de- 
position experiments, with the object of obtaining with gold 
and silver, similar results to those already obtained by Jacobi, 
Jordan, and Spencer with copper, viz. thick deposits of firm, 
coherent metal, bright, and of good colour. As, however, 
there are very few solutions capable of yielding such results, 
their attempts were not at first completely successful. 

At this juncture Mr. Wright met with a passage in 
Scheele's ' Chemical Essays ; (pp. 405 and 406) which soon 



20 The A rt of Electro-Metallurgy. 

proved of the highest de ree of importance to the commer- 
cial success of the art, by enabling suitable deposits of silver 
and gold to be obtained. Speaking of the solubility of the 
oxides and cyanides of gold, silver, and copper, Scheele says 
' If, after these calces' (i.e. the cyanides of gold and silver) 
1 have been precipitated, a sufficient quantity of the precipi- 
tating liquor be added in order to re-dissolve them, the solu- 
tion remains clear in the open air, and in this state the 
aerial acid ' (i.e. the carbonic acid) ' does not precipitate the 
metallic calx.' 

This statement suggested to Mr. Wright the probable 
suitability of the cyanides of gold and silver, dissolved in so- 
lutions of the alkaline cyanides, for the purposes of electro- 
plating • and he immediately took a solution, composed of 
chloride of silver dissolved in aqueous ferro-cyanide of potas- 
sium, and quickly obtained what had never been acquired 
before, viz. a thick deposit of firm and white silver by elec- 
trolytic action. In all previous trials the coating of silver 
had either been very thin, or in a state of dark-coloured, 
loose powder, completely useless for the intended purpose. 

The first article that received the successful coating was 
a small vase, and the next was a small figure of a kid. They 
were coated by Mr. Wright at his residence, and the process 
adopted was as follows : — A common, porous garden-pot, con- 
taining the silver solution, was placed in dilute sulphuric acid 
contained in an outer vessel ; the article to be coated was 
immersed in the inner liquid, and connected by a wire with 
a cylinder of zinc surrounding the porous cell, and im- 
mersed in the dilute acid. It was about a month after 
this that a solution of actual cyanide (not ferro-cyanide) of 
silver and potassium was first employed by Mr. Wright for 
the same purpose. It is true that cyanides in several forms 
had been used both for electro-coppering and silvering about 
sixteen months previously \ but that was by the simple im- 
mersion process, without the use of zinc, or a single cell or bat- 
tery, and by that process no thick deposits can be obtained. 



Discovery of Cyanide Solution. 2 1 

Meanwhile other persons were active in other depart- 
ments of the subject. On March 3, 1840, Joseph Shore 
patented a process by which he deposited copper from a 
neutral solution of its sulphate, and nickel from one of its 
nitrates ' kept of a neutral strength/ by connecting the articles 
by a copper wire with a piece of zinc in dilute sulphuric 
acid ; the two liquids being separated by a partition of 1111- 
glazed earthenware. ' Larger articles are covered separately, 
and small articles, such as iron nails, are placed in a wire 
basket connected by a wire to a zinc plate, and are moved 
from time to time to prevent any parts remaining uncovered.' 

At this period Messrs. G. R. and H. Elkington were 
taking out another patent, dated March 25, 1840, for an 
electro process for coating articles with silver or gold by 
means of the single-cell arrangement, using solutions com- 
posed of oxide of silver dissolved in ' pure ammonia,' or 
prussiate of soda, or other analogous salts ; or oxide of gold 
dissolved in ' prussiate of potash ' by boiling, and kept ' satu- 
rated with gold,' or in ' any soluble prussiate,' or ' any other 
analogous salt' Mr. Wright having submitted his results to 
Messrs. Elkington, these were also embodied by 'them in 
their patent. At first Mr. Wright received a royalty of ore 
shilling per ounce for every ounce of silver deposited ; but 
on his decease, which took place soon afterwards, an annuity 
was paid to his widow. This patent process proved to be 
the basis of all successful electro-plating of gold and silver, 
because it included the solutions of alkaline cyanides, the 
only known liquids that fulfil all the necessary conditions ; 
and the success of those liquids was largely due to their 
alkaline character. From the earliest period of electro- 
plating, german-silver was the substance employed for forming 
the articles which were to be plated. 

On December 8 in the same year Messrs. Elkington took 
out a similar patent in France ; and this was quickly fol- 
lowed, on December 19, by a patent taken out in the same 
country by M. De Ruolz, a French electro-depositor, for 



22 The A rt of Electro-Metallurgy. 

similar objects effected by similar means, viz. electro-gilding 
by means of a solution composed either of cyanide or chlo- 
ride of gold dissolved in the simple cyanide, the ferro-cyanide 
or the ferrid-cyanide of potassium ; the double chloride of gold 
and potassium dissolved in cyanide of potassium \ the double 
chloride of gold and sodium dissolved in soda ; or the sul- 
phide of gold dissolved in neutral sulphide of potassium j 
also electro-silvering by means of a solution of cyanide of silver 
dissolved in cyanide of potassium, each liquid being acted 
upon by means of the voltaic battery. His patent also included 
similar solutions for the electro-deposition of platinum, cop- 
per, lead, tin, cobalt, nickel, and zinc ('Encyclope'die Roret,' 
Galvanoplastie, tome ii., p. 114). A Commission of the 
French Royal Academy of Sciences was appointed to report 
on the new processes of Elkington and De Ruolz, and de- 
cided in favour of Elkington. A dispute also arose between 
the two patentees, which, after a trial at law, was finally set- 
tled by a compromise. 

The chief conditions of success in the process had now 
been attained by the use of the cyanides, but there still re^ 
mained various smaller difficulties to be overcome. In some 
instances the deposited silver would rise in blisters, or por- 
tions would peel off on application of the burnishing tool. 
Tn others the metal assumed objectionable colours, frequently 
brown, yellowish, streaky, or grey ; or, instead of being even 
and smooth, it was covered with asperities, nodules, lines, or 
vertical grooves ; or was of unequal thickness. Great diffi- 
culty was also experienced in coating articles of iron, steel, 
lead, Britannia-metal, &c, so as to secure perfect adhesion ; 
and particularly in coating of an uniform colour and appear- 
ance, articles, the different parts of which were formed of 
several of these metals, or which had been united by different 
kinds of solder. In consequence of these various defects, par- 
ticularly imperfect adhesion and blisters, multitudes of articles 
were returned to the platers. Great opposition was also 
experienced from the manufacturers of Sheffield wares, and 



Early Difficulties of Electro-plating. 23 

shopkeepers who sold plated goods, to the introduction of 
the new articles ; and in consequence of these various diffi- 
culties the process was not remuneiative for at least seven 
years. 

The want of adhesion between the silver and the metal 
beneath, arose partly from the employment of too many cells 
in the battery, but chiefly from want of perfect cleanliness 
of the receiving surfaces. It was eventually overcome by 
cleaning the surfaces with very great care, dipping the 
cleaned article in a very weak solution of mercury imme- 
diately before placing it in the depositing liquid, and lessening 
the number of battery cells. Non-adhesion of the silver was 
especially apt to occur with articles made of Britannia metal, 
and with this particular alloy it was not overcome for several 
years ; it was then remedied by first coating the surfaces 
with copper, by electro-process, in a liquid composed of 
cyanide of copper dissolved in a boiling solution of cyanide 
of potassium, and then silvering them. This method was 
patented by O. W. Barratt, September 8, 1841 ; a different 
and a simpler process is now employed. 

One of the next important additions to the art of electro- 
metallurgy was that made by Mr. Murray (January 1840) ; 
who communicated it orally to the members of the Royal 
Institution, London. It consisted in coating non-conducting, 
surfaces with plumbago, which being an electric conductor 
enabled deposits of metal to be formed by the electro-process 
upon the surfaces of non-conductors, and thus greatly ex- 
tended the sphere of usefulness of the art. During the same 
year also Professor de la Rive made known a process of 
electro-gilding employed by him in the year 1828 ; he gilded 
wires of platinum and silver 'by employing them as negative 
electrodes in a solution of chloride of gold.' (De la Rive's 
'Treatise on Electricity,' vol. hi., p. 546.) 

In the same year also another arrangement of electro- 
depositing apparatus, now known as the ' separate battery ' 
apparatus, was devised by Mr. Mason. In this new arrange- 



24 



The Art of Electro-Metallurgy. 



ment a current from a single cell of a Darnell's battery, A, is 



caused to produce deposition in a separate vessel, B. 
represented by the annexed sketch. 



It is 



Fig. 2. 




In this apparatus, as fast as the metal is removed from 
the solution at the negative pole, by articles being coated, it 
is replaced by an equal amount of metal dissolving at the 
positive pole, or dissolving plate, and the solution, therefore, 
does not require any additional supply of metallic salt. A 
still further modification of Mr. Mason's arrangement was 
soon generally adopted, by substituting any ordinary voltaic 
battery for the single cell of Daniell. 

Another arrangement, termed the 'compound depositing 
cell/ was also devised about this time, by means of which 

Fig. ^. 




the current from a single cell, A, of a battery was caused to 



Separate Battery Process. 2$ 

pass through a series of depositing cells, B (see sketch), and 
thus dissolve and deposit several times the amount of metal 
by the same amount of consumption of zinc and acid ; but it 
was soon abandoned on account of the slowness of action. 

During the year 1841 Mr. Alfred Smee published the 
results of his experiments upon the electro -deposition of 
Antimony, Iridium, Rhodium, Palladium, Platinum, Gold, 
Silver, Copper, Nickel, Iron, Lead, Cadmium, Zinc, &c, in 
the first edition of his book on Electro-metallurgy ; he also 
applied the very appropriate term ' electro-metallurgy ' to the 
process of working in metals by means of electrolysis. In the 
same year also M. De Ruolz electro-deposited brass from a 
solution composed of the cyanides of copper and zinc dis- 
solved in aqueous cyanides of potassium (Walker's ' Electro- 
type Manipulation,' last edition). In the year 1841 also 
Alexander Jones took out a patent (dated January 14) 
relating to electro-deposition, in which he renders a non- 
conducting surface conducting, and fit for receiving electro- 
deposits, by first immersing the article in a solution of nitrate 
of silver, then reducing a film of silver upon it by means of 
a solution of green- vitriol, or by phosphorus either in solution 
or vapour ; or by coating the surface with bronze powder 
or metallic leaf. 

The next event of importance in the history of electro- 
plating consisted in the application of magneto- electricity to 
that object. On August 1, 1842, J. S. Woolrich took out 
a patent for the use of a magneto-electric machine in electro- 
plating, and this machine was used during many years in 
several electro -plating establishments, but has since been 
quite superseded by other magneto-machines of an improved 
kind. During the same year Mr. Palmer patented his ' im- 
provements in producing printing and embossing surfaces/ 
and employed electro-deposition for producing the copper 
plates ; the process was termed ' Glyphography.' Dr. H. R. 
Leeson also took out a patent on June 1, in the same year, 
for improvements in electro-metallurgy, and claimed no less 



26 The A rt of Electro-Metallurgy. 

than about 430 (!) different salts for the purposes of deposi- 
tion. He suggested '• elastic moulds/ formed of glue alone 
or glue mixed with gum, for receiving deposits ; also ' posi- 
tive wires ' led into cavities or under cut parts of the moulds, 
and inserted * conducting wires in wax moulds to facilitate 
deposition ; ; and proposed to keep the articles to be coated 
constantly in motion 'by means of a roasting-jack/ or to 
' agitate the solution.' 

The first use of thermo-electricity appears to be that 
made by Moses Poole, who took out a patent, dated May 
25, 1843, for the use of a thermo-electric pile instead of a 
voltaic-battery for depositing purposes. The method, how- 
ever, did not come into general use. During the following 
year (viz. 1844) a patent was taken out by Napier, dated 
October 22, and one by Parkes, dated October 29. for elec- 
tro-depositing metals from mineral ores and salts whilst in a 
state of fusion. 

The next improvement arose in a singular way. The 
surface of silver deposited from the ordinary cyanide of silver 
and potassium plating solution has a frosted or snow-white 
appearance, and is more or less l chalky ' and dull, and re- 
quires to be burnished or made bright by mechanical means. 
This with articles of highly figured design, or which are 
hollow and require the interior to be bright, is a great disad- 
vantage, because the process of burnishing is tedious, and 
when it has to be applied to the interior of vessels it is also 
very awkward to perform. As with the difficulty of obtain- 
ing thick deposits of firm silver during the early period of 
the electro-process a little circumstance led to that obstacle 
being overcome, so was it with this difficulty, and it hap- 
pened as follows : — In the process of copying figures for 
electro-typing, by moulds composed of a mixture of wax and 
resin, the surface of the mould was covered with a film of 
phosphorus by means of a solution of phosphorus in bisul- 
phide of carbon. It was observed by Mr. W. Milward, at 
Messrs. Elkington's establishment, that when these moulds 



Discovery of Bright -plating. 2J 

were put into the cyanide of silver-plating solution, for the 
purpose of receiving a coating of silver, the silver coating 
upon other articles, such as spoons, forks, &c, which were 
being plated in the same vats, and especially those nearest 
to the moulds, acquired a brightness more or less perfect, 
which occurred sometimes in patches or streaks, and some- 
times extended all over the deposited surface, instead of the 
ordinary snow-white appearance. This circumstance of 
course attracted attention, and induced Mr. Milward to try 
the effect of adding bisulphide of carbon alone to the liquid. 
Considerable success soon resulted ; but at this juncture 
the secret escaped, and in consequence a patent was taken 
out March 2$, 1847, by Mr. Milward and a person of the 
name of Lyons, who had acquired a kr owledge of the secret, 
for producing bright deposited silver by ' adding compounds 
of sulphur or carbon/ bisulphide of carbon being preferred, 
to the cyanide of silver solution. This process has been 
constantly employed ever since, and is now in extensive use. 
Bright copper had also been observed about the year 1845, 
and occurred whenever a large number of phosphorised wax 
moulds were put into a solution of sulphate of copper to re- 
ceive an electro-deposit of copper. In the year 1847 also, 
Professor Silliman copied the iridescent colours of mother- 
of-pearl, by taking a mould of the shell in fusible alloy, and 
then an electro-cast from the mould (' Timbs' Year-Book of 
Facts,' 1847). 

The chief improvements which have been made in 
electro-metallurgy since the year 1847 nave been the gradual 
extension of the process for multiplying printing surfaces, in 
stereotyping, &c, also the production of works of art, &c, 
of increased size in copper, until deposits several tons in 
weight have been attained ; the extensive use of nickel as a 
coating upon harness furniture, &c, the protection of articles 
of cast-iron, ornamental lamp-posts, &c, from rusting, by a 
coating of copper ; the substitution of magneto-electric 
machines, and thermo-electric piles, for voltaic batteries ; the 



2 8 The A rt of Electro-Metallurgy. 

purification of crude copper in the process of copper smelting; 
and, quite recently, the economical production of coppered 
iron rollers for calico printing by means of magneto-electric 
deposition. 



THEORETICAL DIVISION. 

PRINCIPLES AND LAWS UPON WHICH THE ART OF 
ELECTRO-METALLURGY IS BASED. 

The phenomena which occur in electro-metallurgical pro- 
cesses largely involve the principles of dynamic electricity, 
chemico-electric action, electro -chemical action, and also or- 
dinary chemical affinity ; and, if magneto-electric and thermo- 
electric apparatus are also employed, the phenomena then 
include also magneto-electric and thermo-electric action. 

Electric conduction and insulation are involved in 
electro-metallurgical processes, because through all the con- 
ductors, electric generators, and depositing liquids, elec- 
tricity is continually circulating, and requires to be guided in 
its course, and protected from leakage. 

Chemico-electric action, or electric change produced by 
chemical power, is included, because that action is always 
occurring in the voltaic batteries employed. Electro- 
chemical action is also involved because that change is 
constantly going on in the depositing solutions. In the mag- 
neto-machine, magneto-electric induction occurs all the time 
the machine is at work ; and in the thermo-electric pile, 
thermo-electric action, or heat producing electric force, 
operates without cessation. It is evident, then, that a clear 
perception of the principles of these actions is indispensably 
necessary to a proper understanding of the subject. 

electrical principles of electro-metallurgy. 

Conduction and insulation. — Conducting and insulating 
power for electricity, or the capacities of facilitating and 



Conduction arid Insulation. 29 

hindering the passage of electricity, differ in degree in every 
different substance. The best conductor is the worst insu- 
lator, and vice-versa, the degree of the one property being 
inverse to that of the other in every substance. All bodies 
conduct electricity, but in different degrees, and all insulate 
also in different degrees, and the difference of conducting 
power of the best conductor in relation to that of the worst 
is enormous ; and similarly with regard to insulating power. 
The following is a table in which various common sub- 
stances are ranged approximately in the order of their 
relative power of insulating, or hindering the passage of 
electricity ; it commences with the most perfect insulators, 
and ends with the best conductors : — 

1. Ebonite. 20. Chalk. 

2. Shellac. 21. Lime. 

3. Caoutchouc. 22. Dry gases. 

4. Gutta-percha. 23. Dry steam. 

5. Amber. 24. Phosphorus. 

6. Resin. 25. Fatty oils. 

7. Sulphur. 26. Dry metallic oxides. 

8. Wax. 27. Ice at o° C. 

9. Agate. 28. Straw. 

10. Glass. 29. Paper. 

11. Gems. 30. Marble. 

12. Silk. 31. Dry wood. 

13. Wool. 32. Alcohol. Ether. 

14. Hair. 33. Rain-water. 

15. Feathers. 34. Spring- water. 

16. Dry paper. 35. Sea- water. 

17. Leather. 36. Graphite. 

18. Porcelain. 37. Brittle metals. 

19. Camphor. 38. Ductile metals. 

The difference of insulating power or conduction-resist- 
ance between the substances at the two extreme ends of the 
table is extremely great. If the resistance of silver to 
the passage of the current be represented by r, that of a 
rod of gutta-percha, of equal length and diameter, has 



30 



The Art of Electro-Metallurgy. 



been estimated to equal about 850,000,000,000,000,000,000. 
The insulating substances usually employed in electro- 
metallurgy are either gutta-percha, glass, or india-rubber, 
and the wire employed in magneto- electric machines is 
insulated by being covered with cotton or silk. The large 
conductors, to supply the main currents to the vats, are 
covered with gutta-percha or tarred twine. The wires for 
suspending spoons, forks, &c, in the solutions are enclosed 
in tubes of glass. 

The relative conducting powers of pure metals, &c, ac- 
cording to Dr. Matthiessen, are as follows : — 



Silver . 


IOO'O 


Tin . 


12-4 


Copper 


99 '9 


Thallium . 


9-2 


Gold . . . 


77'9 


Lead . 


8-3 


Zinc . 


29-0 


Arsenic 


4-8 


Cadmium 


. 237 


Antimony . 


4-6 


Palladium . 


. i8-4 


Mercury 


i-6 


Platinum 


i8-o 


Bismuth 


I"2 


Cobalt 


172 


Graphite . 


•069 


Iron . 


16-8 


Gas coke . 


•038 


Nickel . 


13-1 


Bunsen's coke . 


•025 



Copper being the cheapest good conductor, very flexible 
and ductile, easily obtainable, and not readily oxidised, is 
nearly always employed for transmitting the current in elec- 
tro-metallurgical operations. Wire composed of iron or of 
brass is rarely used for such a purpose. 

The conductivity of fused salts varies greatly ; if that of 
mercury equals 100,000,000, that of chloride of lead is 
25,300; of iodide of potassium 11,500 ; of nitrate of silver 
8,688 ; of common salt 8,660 ; of potassic carbonate 2,150 ; 
and of chloride of zinc 86 (F. Braun, ' Chemical News,' 
vol. xxx. p. 207). 

The conduction-resistances of liquids are enormous 
in comparison with those of metals. For instance, if that of 
copper at 32 Fahr. is equal to 1, those of various liquids are 
as follows : — 



Conduction-Resistance. 3 1 

Nitric acid at 55° Fahr 976,000 

Sulphuric acid diluted to T T T at 68° Fahr. . . . 1,032,020 

Saturated solution of chloride of sodium at 56 Fahr. . 2 >9°3»538 

,, ,, sulphate of zinc . . . 15,861,267 

,, ,, ,, copper at 48 Fahr. . 16,885,520 

Distilled water at 59 Fahr 6,754,208,000 

According to Dr. Overbeck, if the resistance of water 
equals 390, that of alcohol is 13,000, of ether 40,000, and of 
bisulphide of carbon still greater. Small additions of saline 
matters greatly diminish the resistance of water (' Electrical 
News,' vol. i., p. 170). 

If the conduction-resistance of distilled water is so great 
in relation to that of copper, we can easily understand, by 
referring to the previous table, that the resistance of gases 
must be enormous. The electric conduction-resistance of air 
heated to redness is 30,000 greater than that of water, con- 
taining a 20,000th part of its weight of sulphate of copper 
in solution. The ordinary unit of electrical resistance em- 
ployed in this country is termed an • Ohm ' (see Jenkin's 
'Treatise on Electricity and Magnetism,' p. 158; also 
Appendix, p. 387 of this book). 

Effects of temperature, purity, &>c, upon the electric con- 
ductivity of substances. — The conducting power of substances 
is largely affected by their degree of purity. The least 
admixture of a foreign substance in a metal has a great 
effect ; arsenic in copper is very injurious to electric con- 
duction, and may even increase the resistance as much as 
66 per cent. ; while one half per cent, of iron increases the 
resistance of copper as much as 25 per cent. 

The conducting powers of bodies are also greatly in- 
fluenced by temperature. Warming a metal increases its 
conduction-resistance. Metals usually lose about 30 per 
cent, of conducting-power by rise of temperature from o° C. 
to ioo° C. ; german-silver, however, loses only about 4 per 
cent, by that change. Solid non-metallic substances usually 
increase in conducting power with rise of temperature ; so also 
do liquids almost uniformly, and gases very considerably. 



32 The Art of Electro-Metallurgy. 

Measurements of conduction-resistance are at present 
rarely made in electro-metallurgical operations, but as 
science extends they will probably require to be. The de- 
gree of conduction-resistance in a wire varies directly as its 
length, and inversely as the area of its cross-section. Acids 
and saline liquids obey the same laws of conduction in this 
respect as metals. The methods of measurement of electric 
conduction-resistance are fully described in the treatise on 
'Electricity and Magnetism,' p. 229, by Fleeming Jenkin. 

Heat generated in metals and liquids by co?iduction-?-esist- 
ance. — As heat can produce electricity, so electricity can pro- 
duce heat. It is a general truth of electrical science, that 
wherever an electric current overcomes resistance it produces 
heat. And it therefore not unfrequently happens that, by the 
passage of long- continued and energetic currents, the battery, 
liquids, conducting wires, depositing solutions, the coils of 
wire in magneto-electric machines, the cooler junctions of 
thermo-electric piles, &c, become more or less heated ; and 
these circumstances affect the working. 

Electro -chemical action. — The fundamental basis of elec- 
tro-metallurgy is the fact that, when a current of electricity 
passes through a suitable liquid, it produces a chemical change. 
This phenomenon is called electro-chemical action, because 
electricity is the cause, and chemical action the effect. 
The chief conditions of electro-chemical act'on are that the 
substance must be a liquid, a compound body, a conductor 
of electricity, and traversed by the current. An electrolyte 
(see p. 33) is usually composed of two elementary substances 
— the one a conductor, and the other a non-conductor of elec- 
tricity ; a liquid which is composed either of two conductors 
or two non-conductors does not usually suffer electrolysis. 

The chemical change which takes place consists of a 
chemical decomposition of the liquid , and the constituents 
of the liquid — either primary or secondary — are liberated in 
a free state. The substances are liberated not in the mass 
of the liquid, but at the immediate surfaces of contact of the 



Nomenclature of Electro- Chemical A ction. 3 3 

liquid with the conductors, by which the current enter? and 
leaves the solutions ; and the distance to which the action 
extends from the surface of the conductors into the mass of 
the liquid, is so extremely small, as not to be definitely 
known. 

In all cases of electrolysis the electro-negative elements 
of the liquid, such as metalloids and acids, either combine 
with, or are set free, at the surface of the dissolving or 
positive metal, and the electro-positive elements, such as 
metals and alkalies, either combine with, or are set free or 
deposited, at the surface of the receiving or negative metal. 
For instance, if a piece of silver and a piece of copper are 
immersed in a solution of sulphate of copper, and the current 
from a battery be passed into the solution by means of the 
piece of copper, and out of it by means of the silver, the ne- 
gative elements of the liquid, viz. the sulphuric acid of the 
sulphate of copper, will be separated from its associated 
copper, and will combine with the positive copper terminal, 
causing it to dissolve in the liquid ; while the positive ele- 
ment of the liquid, viz. the copper of the salt, will be depo- 
sited at the surface of the negative or receiving metal, the sil- 
ver, but will not combine with it. But if we substitute a piece 
of platinum for the piece of copper, and mercury for the silver, 
the effects will be reversed ; the acid or negative element will 
collect around the positive platinum, but will not combine 
with it, whilst the positive element of the liquid, the copper, 
will be deposited and combine with the negative mercury. 

Nomenclature of electro-chemical action. —The phenome- 
non of chemical decomposition of a liquid by means of an 
electric current is, in accordance with the nomenclature 
adopted by Faraday, who specially investigated it, called 
electrolysis. The liquid in which it occurs is rallei an 
electrolyte. The conductors immersed in the liquids are 
termed electrodes ; the one by which the current (i.e. the posi- 
tive electricity) enters the liquid is called the anode, or positive 
pole, and that by which it leaves the solution is termed the 

D 



34 The A rt of Electro-Metallurgy. 

cathode, or negative pole. The elements of the liquid which 
are set free by the action are called ions ; those which 
appear at the anode, or positive pole, are called anions, and 
those at the cathode, or negative pole, cations. 

Usual phenomena of electrolysis. — The effects which take 
place at trie two electrodes appear in various forms • in some 
cases a gas is set free and ascends, or it adheres in bubbles 
all over the front surfaces, and round the edge s of the elec- 
trode, or is absorbed by the electrode ; in other instances a 
solid substance is formed, and either adheres to the electrode, 
falls to the bottom of the liquid, or enters into solution. 
Usually the anode dissolves and gradually becomes thinner ; 
sometimes streams of liquid are seen slowly falling from the 
anode to the bottom, or rising from the cathode to the surface 
of the solution, caused by the alteration of specific gravity 
of the layers of liquid in contact with the electrodes, by 
means of electrolysis. Various special phenomena also occur 
in particular cases, which will be mentioned under the heads 
of the deposition of individual substances. 

Decomp os ability of different electrolytes. — Different liquids 
require very different degrees of electric power to decompose 
them. Faraday has given the following order with the sub- 
stances here mentioned, the first named being the most 
easily decomposed : — Solution of iodide of potassium ; 
melted chloride of silver ; melted chloride of zinc ; melted 
chloride of lead ; melted iodide of lead ; hydrochloric acid ; 
dilute sulphuric acid. Smee, in his ' Elements of Electro- 
Metallurgy,' 2nd edition, p. 185, gives nitric acid as the 
most easily decomposable liquid, and other substances in the 
following order : — 

Nitric acid. Dilute sulphuric acid. 

Chloride of gold. Sulphate of cadmium. 

Nitrate of palladium. Sulphate of zinc. 

Chloride of platinum. Sulphate of nickel. 

Nitrate of silver. Sulphate of iron. 

Sulphate of copper. Sulphate of manganese. 

Sulphate of tin. Salts of the alkalies, generally. 



••; Direction of Electrolysis. 35 

T have many times observed that water is decomposed 
before hydrofluoric acid, and hydrochloric acid in preference 
to water ; also selenic acid before selenate of nickel ; but the 
order of decomposability would probably be affected, both by 
pressure, temperature, and degree of dilution. Much investi- 
gation is required in this branch of the subject. 

Direction of electrolysis. — In the electrolysis of any given 
liquid, the substances set free at the anode are always rela- 
tively electro-negative to those set free at the cathode, and 
the latter of course are relatively positive. Anions, therefore, 
are electro-negative and cations are electro-positive sub- 
stances. The negative substances appear at the positive 
pole, or the electrode attached to the copper plate of the 
battery ; and the positive substances at the negative pole, 
or the electrode attached to the zinc of the battery. Metals, 
alkalies, and bases, being electro-positive, are cations, and 
appear at the negative plate ; and metalloids, peroxides, and 
acids, being electro-negative, are anions, and appear at the 
positive one. As the condition! of positive and negative 
are relative, and no substance is absolutely either, the same 
body may sometimes appear at the anode, and on other oc- 
casions at the cathode ; for instance, sulphur when separated 
from a positive body, such as a metal, appears at the anode, 
but when liberated from oxygen, a more negative substance 
than itself, it appears at the cathode. 

Circumstances which affect the quality of electro-deposited 
metals — The physical qualities of the deposited substances 
are largely affected by a number of circumstances ; such as 
the composition of the liquid, its degree of fluidity, tem- 
perature, &c, also the 'density' of the current, or the 
actual quantity of electricity entering a given magnitude of 
surface in a given time ; the rate of deposit ; and, further, 
the condition of the receiving surface. 

The terms employed to designate the quality of the de- 
posited metal refer usually to its mechanical state and colour. 



36 The Art of Electro-Metallurgy. 

By 'reguline' 1 metal is meant that which possesses the ordinary I 
or more perfect metallic qualities of the metal : thus reguline j 
copper is red, bright, and tough ; reguline antimony is grey, 
hard, and crystalline ; amorphous antimony is without 
crystalline structure. The terms, crystalline, sandy metal, 
black powder, &c, are also frequently used. 

Every different solution, and at every different tempera- 
ture, requires to be electrolysed at a different rate, in order 
to deposit its metal from it in any particular desired state 
of aggregation, as crystals, reguline metal, or black powder ; | 
and this is further modified by the form and mechanical state 
of the receiving surface, a rough surface, or one covered 
With points, or having ragged edges, requires a slower rate of 
deposition than a smooth one, in order to obtain regufine 
metal. A large amount of experimental investigation remains 
to be made also in this part of the subject. 

The circumstance which most affects the quality (and 
purity) of the deposited metal is the composition of the elec- 
trolyte. By far the greater number of solutions yield up 
their metal only in the form of a black powder, however 
carefully the process be conducted. From only a very few 
liquids are metals deposited in their ordinary or reguline j 
state, and only a few of the metals have yet been obtained in 
that condition in thick masses. Copper, antimony, and silver 
are the easiest to obtain in thick layers ; I have obtained 
reguline deposits of antimony 1^ inch in thickness. Zinc, 
gold, platinum, tin, nickel, cadmium, and lead are usually 
only obtained in thin reguline films, or in roughly aggregated 
nodules or crystalline forms ; and most of the other metals | 
have been only obtained in the state of a dark powder. 
The degree of fluidity and diffusive power of the electrolyte 
also affects the deposit ; a thick, immobile, non-diffusive 
liquid will adhere to the cathode after the layer next that 
electrode has been deprived of its metal, and thus alter its 

1 The term ' reguline ' differs from ' regulus ; ' the latter means metal 
which has been reduced from its ores by means of fusion and a fiux. 



Quality of Electro-Deposited Metals. 37 

quality. Some solutions also will only yield reguline metal 
whilst they are hot, or whilst being stirred. 

A paper was read at the meeting of the British Associa- 
tion, at Bradford, by Dr. Gladstone, on ' Black Deposits of 
Metals,' in which he remarks that the allied metals, platinum, 
palladium, and iridium are generally, if not always, black 
when precipitated by substitution (i.e. by single immersion 
process), and bismuth and antimony form black fringes and 
little else ; similar fringes are also formed by gold ; but it 
also yields green, yellow, or lilac-coloured metal according 
to circumstances. Copper, when first precipitated on zinc, 
whether from a weak or strong solution, is black • but in the 
latter case it becomes chocolate-coloured as it advances, or 
red if the action be more rapid. Lead, in like manner, is 
always deposited black in the first instance, though the grow- 
ing crystals become of the well-known dull grey. Silver and 
thallium appear as little bushes of black metal on the de- 
composing plate if the solution be very weak, otherwise they 
grow of their proper colour. Zinc and cadmium give a black 
coating, quickly passing into grey when their weak solutions 
are decomposed by magnesium. The general result may be 
stated thus : if a piece of metal be immersed in the solution 
of another metal which it can displace, the latter metal imme- 
diately makes its appearance at myriads of points in a con- 
dition that does not reflect light ; but as the most favourably 
circumstanced crystals grow, they acquire the optical proper- 
ties of the massive metal, the period at which the change 
takes place depending partly on the nature of the metal, and 
partly on the rapidity of its growth (' Telegraphic Journal,' 
vol. i., p. 302). 

Some metals are especially liable to crack and curl up 
whilst being deposited ; this is the case in a strong degree 
with antimony, and less so, but conspicuously, with iron and 
nickel. Others form very hard and tenacious deposits ; that 
of iron is extremely hard, and of nickel so much so that it 
cannot be burnished, and if scratch-brushed it becomes quite 



38 , The Art of Ekctro-Metalliirgy. 

yellow by tearing off particles of the brass scratch-brushes. 
Electro-deposited copper, and even gold, is also sometimes 
remarkably hard. All electro-deposited metals are more or 
less crystalline or porous, and can rarely be made to form 
air-tight, or even water-tight, vessels without annealing, es- 
pecially if the layer of metal first deposited is scraped or 
filed away ; electro-deposits therefore do not protect metallic 
surfaces from oxidation, like a coating of the same metal put 
upon them by a process of fusion. They are also more 
porous on their outer surfaces, i.e. the side last deposited, 
than upon their inner, and if heated in a fire will often become 
concave on the side last deposited. Seams also cannot 
be closed (or edges joined together) by electro-deposition ; 
they always became larger ; even a scratch will gradually 
become a deep groove. 

Influence of density of the current. — Next to the composi- 
tion of the liquid, the circumstance which most affects the 
quality of the deposit is what has been termed the ' density 
of the current,' or the actual quantity of electricity entering 
a given area of receiving surface in a given time. With 
a good depositing solution, a non-oxidisable metal, if the 
density of the current is great, is deposited as a black powder ;. 
if it is small the metal assumes the form of crystals, or is- 
precipitated in the state of a subsalt ; and between these two 
extremes, the soft, reguline, hard, and sandy deposits occur. 
A saturated solution of sulphate of copper, acidulated with 
dilute sulphuric acid, yields good reguline metal when the 
metal is deposited from it at the rate of about half an ounce 
per square foot of surface per hour. The density of the cur- 
rent affects not only the quality of the liberated cations, but 
also that of the anions, as has been already observed (see 
'Telegraphic Journal,' vol. if., p. 178) in the instance of- 
oxygen, also with chlorine. 

The effect of small density of the current is different 
with solutions of the noble metals to what it is with those of 
the base ones, because the latter metals are easily oxidised 



Formation of Metallic Crystals. 39 

and the former are not. With solutions of noble metals 
a current of small density deposits the metal in the form of 
crystals, but with those of the base ones it deposits an oxide, 
or even a subsalt, instead of the metal. And as the current 
is strongest at its first commencement and is then weakened, 
first by polarisation and subsequently by the deposition of 
the less-conducting layer, the deposit rapidly changes in 
many cases from good reguline metal to a non-adherent 
coating of oxide or salt. Solutions of nickel are very apt 
to show this change (p. 232). 

A perfectly smooth, bright surface is the best to receive a 
deposit ; if the surface is rough the deposit will be rough 
also. As a deposit increases in thickness it becomes more 
and more uneven, and therefore, in nearly all cases, the 
deposit sooner or later, and in most cases very quickly, loses 
its reguline character and brightness, and becomes a layer of 
either black or crystalline powder ; the edges of the cathode 
which receive the thickest deposit are the soonest affected. 

Formation of ?netallic crystals. — Every different metal, 
and even the same metal when deposited from different solu- 
tions, gives a different form of crystal. In some solutions — 
chloride of tin for example — crystals form with great rapidity. 
The annexed figures represent the forms of crystals of silver, 
tin, and gold ; they are copied from Dr. Gladstone's Lectures, 
' Telegraphic Journal,' vol. hi., pp. 29 and 38. Fig. 4 repre- 
sents silver deposited from a weak solution of nitrate of 
silver ; Fig. 5, ditto, from a strong solution ; Fig. 6, from a 
very strong solution ; Figs. 7 and 8, from a nearly exhausted 
solution ; and Fig. 9 from a 2^ per cent, solution. Fig. 10 
shows tin, deposited from a solution of chloride of tin ; and 
Fig. n, gold, from a solution of chloride of gold. 

Ci?'cumstances which a feet the quantity of electro-deposited 
metal. — In a liquid which yields at the cathode a single 
metal only, the quantity of the particular metal set free 
depends entirely upon the amount of electricity which has 
passed ; but with different metals it depends also upon what 



40 The A rt of Electro-Metallurgy. 





FIG.6. 



FIG. 9. 















FIG. 10. 








FI&.B. 



Fit. 11. 



Quantity of Electro-Deposited Metals. 



41 



is termed the valency of the metal and upon its atomic 
weight ; by valency is meant the amount of chemical force 
associated with an atom. 

. This part of the subject requires on the part of the 
student a certain amount of knowledge of chemistry ; and 
as this book is not one on that subject, I assume that the 
student already possesses a sufficient preparatory acquaint- 
ance with chemistry to enable him to enter on the subject 
of electro-metallurgy ; that he is, for instance, acquainted 
with the chief properties of the commoner elementary 
substances, and of their chief compounds , of acids, bases 
and alkalies, of the meaning of the terms specific gravity, 
molecular weight, combining and equivalent proportions, 
molecular gaseous volumes, &c; but, if he is not, I must 
refer him to Miller's ' Inorganic Chemistry/ published in this 
series of text- books. I therefore only insert in this treatise 
such chemical information as I consider must not be omitted. 

Relation of chemical Value, or valency of afoms, to electro- 
lysis. — In accordance with the doctrines of chemistry, the 
elementary substances are classed into Monads, Dyads, 
Triads, Tetrads, &c., as in the following table : — 



MONADS 


DYADS 


TRIADS 


TETRADS 


II EX ADS 


Hydrogen 


Oxygen 


Nitrogen 


Carbon 


Molybdenum 


Lithium 


Sulphur 


Boron 


Silicon 


Vanadium 


Fluorine 


Selenium 


Phosphorus 


Titanium 


Tungsten 


Chlorine 


Tellurium 


Arsenic 


Tin 


Osmium 


Bromine 


Barium 


Antimony 


Zirconium 


Chromium 


Iodine 


Strontium 


Rhodium 


Thorinum 


Manganese 


Caesium 


Calcium 


Gold 


Cerium 




Rubidium 


Lanthanum 


Bismuth 


Iron 




Potassium 


Didymium 


Aluminium 


Nickel 




Sodium 


Glucinum 


Indium 


Cobalt 


1 


Thallium 


Magnesium 




Uranium 




Silver 


Zinc 

Cadmium 
Copper 
Mercury 




Lead 

Ruthenium 

Iridium 

Palladium 

Platinum 


1 



42 



The Art of Electro- Metallurgy. 



A monad is an elementary substance, one atom of which 
possesses one equivalent of chemical power • a dyad is one, 
an atom of which possesses two such equivalents ; a triad 
three ; a tetrad four, &c. One atomic weight therefore of 
a dyad element is chemically equivalent to two of a monad 
element ; one such weight of a triad element is chemically 
equivalent to three of a monad, or one and a half of a dyad ; 
one of a tetrad is equivalent to four of a monad, two of a 
dyad, or one and a third of a triad ; and so on. 

Equivalency of electro-chemical action. — As substances 
by chemical union unite in certain definite proportions by 
weight, it follows as a matter of course that when a chem- 
ical compound is decomposed, the separated ingredients 
mast also possess definite proportions by weight. When, 
therefore, by the passing of a current of electricity through 
a compound conducting liquid, elementary substances are 
liberated at the electrodes, they are set free in their chemi- 
cally equivalent proportions by weight. And as the chemi- 
cally equivalent proportions are either the same as their 
atomic weights, or are some simple submultiple of them, 
the following table of atomic weights is inserted for the 
purpose of reference : — 

Symbols and Atomic Weights of Elementary Substances. 



Name 


Symbol 


Atm.Wt. 


Name 


Symbol 


Atm. Wti 


Aluminium 


Al 


27-5 


Copper . 


Cu 


63'5 


Antimony 


Sb 


122' 


Didyiniura 


D 


96 • 


Arsenic . 


As 


75- 


Erbium . 


E 


(?) 


Barium . 


Ba 


137' 


Fluorine , 


F 


IQ- 


Bismuth . 


Bi 


2IO- 


Glucinum 


G 


9-3 


Boron 


B 


io- 9 


Gold 


Au 


196-6 


Bromine . 


Br 


8o- 


Hydrogen 


H 


i- 


Cadmium 


Cd 


112- 


Indium . 


In 


JI 3'4 


Caesium . 


Cs 


*33' 


Iodine 


I 


127; 


Calcium . 


Ca 


40- j 


Iridium . 


Ir 


197- 


Carbon . 


C 


12- 


Iron . 


Fe 


56- 
92- 


Cerium . 


Ce 


Q2- 


Lanthanum 


La 


Chlorine . 


CI 


35*5 


Lead 


Pb 


207- 


Chromium 


Cr 


5--5 


Lithium . 


L 


V 


Cobalt . 


Co 


59- 


Magnesium 


Mg 


24 '3 



Equivalency of Electro- Chemical Action. 43 



Symbols and Atomic Weights of Elementary Substances — continued 



Name 


Symbol 


Atm. Wt. 


Name 


Symbol 

Ag 


1 
Atm. Wt. 


Manganese 


Mn 


55' 


Silver 


108* 


Mercury . 


Hg 


200 • 


Sodium ; 


Na 


23- 


Molybdenum . 


Mo 


9 6- 


Strontium 


Sr 


87-5 


Nickel . 


Ni 


59- 


Sulphur . 


S 


32- 


Niobium . 


Nb 


975 


Tantalum 


Ta 


138- 


N itrogen 


N 


14* 


Tellurium 


Te 


129- 


Osmium . 


Os 


199' 


Thallium 


Tl 


204- 


Oxygen . 


O 


16- 


Thorinum 


Th 


119- 


Palladium 


Pd 


106-5 


Tin 


Sn 


u8- 


Phosphorus 


P 


Si" 


Titanium 


Ti 


5o* 


Platinum 


Pt 


197' 


Tungsten 


W 


184- 


Potassium 


K 


39'i 


Uranium 


U 


120' 


Rhodium 


Ro 


104-3 


Vanadium 


V 


*37' 


Rubidium 


Rb 


85- 


Yttrium . 


Y 


(?) 


Ruthenium 


Ru 


104-2 


Zinc 


Zn 


65- 


Selenium 


Se 


79'5 


Zirconium 


Zr 


89 5 


Silicon . 


Si 


28- 









As a monad exerts one equivalent of chemical force, a 
dyad two, a triad three, &c, and the elementary substances 
set free at the two electrodes are liberated in their chemically 
equivalent proportions, it follows chat when compounds are 
decomposed by an electric current, for each atomic weight 
of a dyad set free at one electrode, two of a monad, or one 
of a dyad, are liberated at the other ; similarly when an 
atomic weight of a triad is separated at one pole, three of a 
monad, or one and a half of a dyad, are separated at the 
other, and so on ; for instance, in the electrolysis of strong 
hydrochloric acid, one part by weight of hydrogen is set 
free at the cathode, and thirty- five and a half parts of 
chlorine at the anode. In the electrolysis of water two 
parts by weight of hydrogen appear at the cathode and 
sixteen parts of oxygen at the anode, and so on. 

Frequently, however, the substances which are set free, 
or appear at the electrodes, are not simple elements, but 
compound bodies, and even mixtures of compounds ; but in 
these cases also a similar principle of chemical equivalency 



44 The A ri of Electro-Metallurgy. 

operates, and we may say generally, whatever substance, or 
mixture of substances, are set free at one electrode, a chemically 
equivalent weight of substances of opposite electrical nature is 
set free at the other. 

Definite electro-chemical action. — Not only are the element- 
ary and compound substances which are set free at the two 
electrodes, by the electrolysis of a given liquid, liberated in 
definite proportions by weight, which are identical with their 
chemically combining or equivalent proportions, but also, if 
the same current is made to traverse a series of different 
liquids, the chemical actions in all of them are also in chem- 
ically equivalent quantities'; and therefore produced by the 
same amount of electricity. This great truth was discovered 
by Faraday. 

The same amount of electricity which will decompose 
one molecule or eighteen parts of water, setting free two 
parts by weight of hydrogen and sixteen parts of oxygen in 
one vessel, will decompose two molecules or seventy-three 
parts of hydrochloric acid, setting free two parts of hy- 
drogen and seventy-one parts of chlorine in another. If 
we cause the same current to pass through a solution 
of cyanide of silver and potassium, then through one of 
sulphate of copper, and finally through one of antimony, 
each solution being prepared and acted upon so as to yield 
only pure metal, we find that for every 108 parts of silver 

deposited in the first vessel, 3175 parts ( or -^5 ) of copper 

are set free in the second one ; and 40*66 parts (or -1^^ 

of antimony in the third one. 

By employing this method of passing the same current 
or amount of electricity through successive solutions, and 
weighing the products set free, their relative chemical equiva- 
lents may be found : for instance, I passed a voltaic current 
through a solution which deposited pure copper only, and 
through another which deposited pure antimony alone, and 



Theory cf Electrolysis. 45 

weighed the amounts of deposit. The weight of the copper 
obtained was 317 grains, and of the antimony 40-6 grains, 
which is equal to one atomic, weight or 63-5 parts of copper, 
as the equivalent of 81*32 parts of antimony, or two-thirds 
an atomic weight of that metal=i2i*98 as the full atomic 
weight of antimony. 

Theory of electrolysis. — Faraday considered that elec- 
trolytic decomposition is the result of a peculiar corpuscular 
action developed in the direction of the current ; it proceeds 
from a force which is either added to the affinity of the bodies 
present or determines the direction of that force. The elec- 
trolyte is a mass of acting particles, of which all that are in 
the course of the current contribute to the terminal action ; 
and in consequence of the affinity between the elements 
being weakened or partially neutralised by the current 
parallel to its own course in one direction, and strengthened 
and assisted in the other, the combined particles acquire a 
tendency to move in different directions. The particles of 
one element, a, cannot travel from one pole to the other un- 
less they meet with particles of an opposed substance, b, ready 
to move in the opposite direction. For in consequence of 
their increased affinity for these particles, and the diminu- 
tion of their affinity for those which they have left behind 
them in their way, they are continually driven forward. 

In addition to the law of definite electro-chemical action 
Faraday has advanced what is termed the binary theory of 
electrolysis— that 'only those compounds of the first order 
are directly decomposable by the electric current, which con- 
tain one atom of one of their elements for each atom of the 
other ; for instance, compounds containing one atom of hy- 
drogen or metal with one atom of oxygen, iodine, bromine, 
chlorine, fluorine, or cyanogen,' whilst ' boracic anhydride 
(B0 3 ), sulphurous anhydride (S0 2 ), sulphuric anhydride 
(S0 3 ), iodide of sulphur, chloride of phosphorus (PC1 3 ) 
and (PCI5), chloride of sulphur (S. 2 C1), chloride of carbon 
(C 4 C1 6 ), tetrachloride of tin (SnCl 4 ), terchloride of arsenic 



46 The A rt of Electro- Metallurgy. 

(AsCl 3 ), pentachloride of antimony (SbCl 5 )/ are non'con- 
ductors of electricity, and incapable of electrolysis. 

Secondary effects of electrolysis. — Very frequently the sub- 
stances which appear at the electrodes are not those ori- 
ginally set free, but are liberated, or set free, by the action of 
the originally liberated bodies upon the liquid or upon the 
electrode. Some substances which are not of the simple 
binary character mentioned are decomposed by current 
electricity, and yield their positive and negative elements in 
equivalent proportions at their respective electrodes ; but 
according to this theory they are indirectly decomposed, i.e. 
they are decomposed by the chemical action of some of 
the elements set free by the direct action of the current upon 
other substances present. For instance, ' fused borax 
(biborate of soda Na 2 0, 2BO3) yields oxygen gas at the 
anode and boron at the cathode ; now, since fused boracic 
acid is not decomposed by the electric current, the separation 
of the boron must be attributed to indirect action ; the cur- 
rent resolves the soda (Na 2 0) into oxygen and sodium, and 
the latter separates boron from the boracic acid ; (Faraday). 
In a similar way a solution of common salt yields chlorine 
at the anode, and hydrogen and soda at the cathode. 
The salt is probably first decomposed into chlorine and 
sodium, and the liberated sodium decomposes the water, 
forming soda and setting free hydrogen, for when the cathode 
consists of mercuiy, an amalgam of sodium is obtained. In 
other cases, as that of a solution of sulphate of copper, nitrate 
of silver, or chloride of gold, the hydrogen produced by the 
decomposition of the water deoxidises the metallic salts in 
solution, setting free their metals and reconstituting water. 
Similar secondary actions take place at the anode ; if that elec- 
trode is formed of an easily corrodible metal the elements set 
free at its surface combine with it, and form a new compound. 
In other cases where the electrode is not corroded, as an 
anode of platinum in a solution of nitrate of silver or acetate 
of lead, the liberated oxygen sometimes converts the salt into 






A Hoy of Electro- Deposits with Electrode. 47 



an insoluble peroxide, which adheres to the anode. Second- 
ary effects at the anode may sometimes be avoided by the 
employment of an anode of platinum or gas-carbon. 

Alloy of deposits with the cathode and with each other. — • 
When a perfectly clean surface of a metal receives a deposit 
by electrolysis, in the great majority of cases, the first portions 
of the metal deposited penetrate into the receiving surface, 
and form either a mixture or alloy. I have met with some 
new instances of this kind. I deposited a thick coating of 
copper on the outside of a platinum cup. After heating this 
cup to low redness a few times, the coating became loose, 
and I tore it all off and digested the platinum surface in 
nitric acid, and washed it ; it then looked perfectly free from 
copper. On heating it again to low redness its surface became 
black with oxide of copper. I cleaned it again in a similar 
manner and heated it once more ; the surface again became 
black. In this way, even after cleaning and heating six or eight 
times, copper appeared ; the copper, therefore, must have 
passed deeply into the substance of the platinum, and diffused 
again outwards in the process of heating In another in- 
stance a piece of thick platinum foil, upon which I had de- 
posited a film of tellurium in dilute chloride of tellarium, with 
a tellurium anode and a current from five Smee's cells, was 
scraped very clean from the deposit and heated to low red- 
ness. An easily-fusible alloy was formed upon the surface, 
and was oxidised and reduced repeatedly in the flame of a 
Bunsen's burner, as if the tellurium had soaked into the 
platinum. 

Sonstadt also observed that a platinum crucible which had 
been thinly electro-gilded lost its golden appearance by 
heating to a moderate redness, by the gold soaking as it 
were into the platinum (Weldon's ' Register,' No. 36, July 
1863, p. 498). In the process termed 'pyroplating' also, an 
electro deposited layer of gold upon steel nearly disappears on 
heating the steel article ; a second layer behaves similarly but 
to a less extent ; a third does not disappear at all (' Chemical 



48 The Art of Electro-Metallurgy. 

News,' vol. xxvi., p. 137). The first films of one metal electro- 
deposited upon another frequently form an alloy, even with- 
out the aid of heat ; for instance, films of zinc or cadmium f 
deposited upon copper impart to its surface a yellow colour, 
and in other cases similar effects probably occur, but do not 
happen to be observable. If one of the metals happens to 
be a liquid or a gas the effect is often more perfect ; thus 
most metals, even those of the earths and alkalies, when 
deposited upon mercury are absorbed by it and form \ 
amalgams ; hydrogen also, when deposited upon palladium, 
iron, and the surfaces of various metals, penetrates deeply 
into tnem, and alters their properties. This diffusive action 
of one metal within another operates not only during the 
process of deposition, but continues afterwards ; thus a yellow 
film of alloy, obtained by depositing copper upon zinc or 
cadmium, disappears in a few weeks, as if absorbed by the 
metallic substratum. This formation of metallic compounds 
takes place also, and even more completely, when two metals 
are simultaneously electro-deposited. In this way the less 
easily reducible metals, such as nickel, and iron, in the 
electro-deposition of which hydrogen is simultaneously de- 
posited, are very liable to contain hydrogen ; and in the f 
case of nickel this enclosed gas is said to sometimes cause 
the deposit to split and curl up, and separate in brilliant 
films (Sprague's ' Electro- Metallurgy/ p. 305). In the 
case of antimony, especially that deposited from the bromide 
and iodide, large bubbles of gas gradually accumulate upon 
the surface of the deposit, and the deposited metal is full of 
them. The explosive character of some electro-deposits is [ 
also probably due to absorbed hydrogen. I have been in- 
formed that zinc which had been electro-deposited in a grey- 
black, spongy mass upon the iron plates of an exhausted 
battery, consisting of ten pairs of zinc and iron plates, ex- 
ploded when struck ; but I several times attempted with- 
out success to obtain such a deposit. Napier, in his ' Electro- 
Metallurgy,' 5th edition, p. 182, speaks of explosive electro- 



Purity of Electro-Deposited Metals. 49 

deposited bismuth. A writer in Dingler's 'Polytechnic 
Journal' also speaks of electro-deposits of rhodium and iridium 
exploding when struck (' Journal of the Chemical Society/ 
vol. ii., p. 1007). 

The absorption of electro-deposited hydrogen has a great 
effect upon the properties of iron and steel. ' If after im- 
mersion, say, ten minutes in either sulphuric or hydrochloric 
acid, a piece of iron or steel be tested, its tensile strength 
and resistance to torsion will be found to be diminished. 
Exposure to the air for several days, or gentle heat, will 
however restore its original strength ' (W. H. Johnson, 
'Chemical News,' vol. xxvii.,pp. 82 and 176; also vol. xxix., 
pp. 89 and 213 ; also Professor O. Reynolds, p. 118 of the 
same volume. Compare also the paragraphs on electro- 
deposition of hydrogen and its absorption by deposited 
metals, pp. 96, 247). 

As steam boilers are occasionally supplied with water 
containing traces of acids, and the degree of acidity of the 
water becomes stronger by the evolution of steam, it is 
reasonable to suppose that the deposition of hydrogen by the 
simple immersion process, and its absorption by the iron, 
may in some cases contribute to the bursting of those 
vessels ; and in such cases the electro-deposition of hydrogen 
is a circumstance not to be neglected. 

Purity of electi'o- deposited metals. — Electro-deposited 
metals are by no means necessarily pure ; they rarely are 
so, and the reason, probably, why the popular notion has 
arisen that they are very pure is because copper is the 
metal most frequently deposited, and such copper happens 
to be an exceptional instance of purity. The degree of 
purity of deposited metals depends chiefly upon the degree 
of purity of the solution ; if that is pure the deposit is likely 
to be so, and will be so unless it unites with the hydrogen 
liberated simultaneously with it, or with any of the constitu- 
ents of the liquid, as in the instance of amorphous or ' ex- 
plosive antimony.' The purity of the solution largely de- 

E 



5 o The A rt of Electro-Metallurgy. 

pends upon the circumstance whether the anode is pure, and 
whether its impurities are soluble in the liquid ; if they are 
not, they cannot be deposited ; if they are soluble, then their 
deposition or not will largely depend upon the circumstances 
mentioned in the immediately following and preceding para- 
graphs. The great purity of electro-deposited copper is 
largely dependent upon the fact that any lead contained in 
the anode is insoluble in a sulphate solution, and any zinc i 
contained in it is too electro-positive in an acid solution to 
be thrown down with the copper. 

Electrolysis of mixed liquids. — Of the electrolysis of mixed j 
metallic solutions comparatively little is known ; if, however, 
a solution contains several dissolved metals of very different 
degrees of positive electric capacity, the least positive metal 
is usually deposited first, unless there is an insufficient 
amount of that metal present to convey the whole of the 
current ; and if the current is continued till the whole of the 
metals are deposited, the most positive one is the last to be , 
liberated. It is probable, also, that if the metals are about \ 
equally positive in the particular liquid, and their salts possess 
an approximately equal degree of conducting power, and 
are not widely different in quantity, the current divides itself I 
between them, and is conducted by each ; but much investi- ! 
gation needs to be made in this part of the subject. 

Electro-deposition of alloys. — It is much more difficult to 
deposit zinc than copper, because zinc is more electro-posi- j 
tive ; it is still more difficult to deposit two metals than one, 
especially if one of the metals is highly electro-positive to j 
the other, as zinc usually is to copper, and it can only be I 
effected by selecting a liquid in which the one metal is but 
feebly electro-positive to the other. According to the late 
eminent investigator. Professor Magnus, the separate and 
simultaneous deposition of substances from a mixed solution j 
depends : ist, on the density of the current ; 2nd, on the j 
proportions in which the different substances exist in the 
fluid ; 3rd, on the nature of the electrodes \ and 4th, on the 



Electro-Deposition of A Hoys. 5 1 

greater or less facility with which one or the other substance 
can be carried from stratum to stratum within the fluid ; as 
well as on the obstacles which stand in the way of this 
transmission, either in the shape of porous walls or in any 
other form (' Philosophical Magazine/ 4th series, vol. xii., 

P- 159)- 

With solutions in which alloys are to be deposited the 
most important condition is, that neither of the metals to be 
deposited shall be electro-positive to the other in that liquid. 
This is best tested by taking a wire of each metal, connecting 
them with a galvanometer, and simultaneously immersing 
their free ends in the liquid ; if either is electro-positive the 
needle of the instrument will be deflected, while the amount 
of deflection will indicate the amount of their electric differ- 
ence in that liquid. It may also be tested by immersing a 
wire of each metal (not in mutual contact) in the liquid ; if 
either become coated with the other metal in one hour, that 
one is positive ; but if neither becomes coated in six hours, 
there is probably no considerable electric difference between 
them. 

The following experiments of mine show that if a liquid 
contains two metals in solution, and a wire or other piece of 
each of those metals is immersed in the liquid, and one 
becomes coated with a deposit of metal, while the other does 
not, the coated one is electro-positive to the other in that 
liquid, and the solution will only yield by means of a feeble 
separate current the same metal which is deposited by simple 
immersion. 

First experiment. — With an alloy solution, consisting of 
equal measures of a strong solution of protochloride of tin, 
and terchloride of antimony, with an anode either of tin or 
of antimony (the latter is the more suitable because it does 
not become coated by simple immersion in the liquid), a 
copper cathode, and a single cell of small Smee's battery, only 
antimony was deposited ; the tin became coated with anti- 

E2 



5 2 The A rt of Electro-Metallurgy. 

mony by simple immersion, and was found by the galvano- 
meter to be strongly positive to that metal. 

Second experiment. — With a liquid composed of equal 
measures of a solution of protochloride of tin and chloride 
of bismuth, and either a bismuth or tin anode (the former 
is the best), a brass cathode, and a small single cell of 
Smee's battery, only bismuth was found to be deposited ; the 
tin was positive to the bismuth by the galvanometer, and 
became coated quickly with that metal by simple immersion. 

Third experiment. — With a mixture of equal measures 
of terchloride of antimony and chloride of bismuth, antimony 
anode, copper cathode, and a feeble Smee's battery, only 
antimony was deposited; bismuth became slowly coated 
with antimony in the solution by simple immersion, and was 
found by the galvanometer to be moderately positive to the 
latter metal in it. 

Fourth experiment. — With ioo grains each of proto- 
chloride of tin and chloride of zinc dissolved together in an 
ounce of distilled water, tin anode, copper cathode, and one 
small Smee's cell, only tin was deposited ; zinc was positive 
to tin in this liquid by the galvanometer, and deposited tin 
upon itself by simple immersion. 

Fifth experiment. — With equal measures of strong solu- 
tions of nitrate of zinc, and ternitrate of bismuth, and a 
little nitric acid, bismuth anode, copper cathode, and a 
feeble one-pair battery, only bismuth was deposited ; zinc 
was strongly positive to bismuth in this liquid by the galva- 
nometer, and became quickly coated with that metal by 
simple immersion. 

Sixth experiment. — With a solution of mixed sulphates 
of zinc and copper, copper anode and cathode, and a single 
small battery, copper alone was deposited ; zinc was strongly 
positive to copper in this liquid by the galvanometer, and 
coated itself immediately with copper in it by simple 
immersion. 

Further, if we take some distilled water, and dissolve 



Electro-Deposition of Alloys. 53 

some caustic potash in it, and pass a moderately-strong 
current through it by platinum electrodes, hydrogen gas 
will alone be set free at the cathode ; in this case also 
the least positive of the two elements of the liquid — potas- 
sium and hydrogen — is set free or deposited. If we now 
add a little sulphuric acid to the solution to neutralise and 
convert it into a solution of sulphate of potash, add some 
sulphate of zinc besides, and pass a weak current through 
the liquid, we shall obtain a deposit of zinc on the cathode, 
but no hydrogen or potassium. In this case we cannot de- 
termine by the galvanometer which is the most positive in 
this liquid, hydrogen or zinc, because the former is a gas ; 
but it is probable that hydrogen is most positive, because 
the zinc does not evolve it by simple immersion in this liquid. 

If we further add to the liquid a small quantity of sul- 
phate of copper, and treat it as before, neither potassium, 
hydrogen, nor zinc will be deposited, but only copper ; we 
also find by the galvanometer that copper is less positive than 
zinc in such a liquid, and that zinc coats itself with copper 
in it by simple immersion ; in this case also the least positive 
of the positive elements is alone deposited. From these and 
many other experiments which I have made with similar 
results we deduce the following rule : — If a liquid contains 
several metals or electro- positive substances, and a weak 
electric current is passed through it, only that substance 
which is the least electro-positive will be deposited. 

With regard to the influence exercised by the proportions 
of the ingredients of the liquid, and the strength of the cur- 
rent, I may observe that if the liquid contains several metal- 
dissolved in equal quantities, and only one is being deposited 
by the passage of a weak current, a considerable increase in 
the strength of current will cause a portion of the next more 
positive metal to be deposited along with the less positive 
one ; but this alloy deposit will not be very coherent, because 
the power required to deposit the second metal in the regu- 
line state will be so great as to deposit the first as a soft 



5 4 The A rt of Electro- Metallurgy. 

powder ; and this holds most true when the difference of elec- 
tric power required is the greatest. Thus, ist, if sroall quan- 
tities of sulphate of zinc and sulphate of copper are dissolved 
together in a large quantity of water, and a feeble current 
passed through the solution, only reguline copper will be 
deposited; but if the current passing be considerably in- 
creased, the deposit of copper will cease to be reguline, and 
zinc will be deposited with it. If the power be still further 
increased, hydrogen gas will also be evolved at the surface 
of the deposited metals. 2nd, if we dissolve a small quan- 
tity of sulphate of copper and a large quantity of sulphate of 
zinc in a large quantity of water, and pass a strong current 
through the solution, copper, zinc, and hydrogen will be set 
free at the cathode. 3rd, if we slightly moisten a lump of 
caustic potash with pure water, and pass a weak current 
through it by platinum electrodes, hydrogen alone will be set 
free at the cathode ; but if a very powerful current is em- 
ployed, potassium also will be deposited. In each of these 
cases we find that when the current is least dense the least 
positive of the positive substances is alone deposited ; but 
if the power is sufficiently increased, and there is only a small 
portion of the less positive substance present, the more po- 
sitive substances, even though they are much more positive, 
will also be deposited. The weaker affinities are overcome 
first and to the greatest extent ; the current of electricity ex- 
ercising its influence first, and in the greatest proportions, 
upon the salt of the least positive metal. 

Polarisation of electrodes. — After an electric current has 
been passing for some time between two electrodes in a 
liquid, if the electrodes be separated from the source of the 
current, and whilst they remain undisturbed in the liquid be 
connected with a galvanometer, a current occurs, and in a 
reverse direction to that of the original one. It often also 
occurs, but to a less extent, if the two electrodes are trans- 
ferred to another liquid, or if two fresh electrodes are care- 
fully immersed in the corresponding parts of the same liquid. 



Peroxides 07i Anodes. Electrolytic Movements. 55 

This phenomenon, known as a ' polarisation,' continually 
occurs in electro-metallurgical processes, and may be ex- 
plained as follows : — the various substances, either primarily 
liberated, or secondarily formed, at the two electrodes, either 
adhere in a solid state to the electrodes, or fall to the 
bottom, or dissolve in the liquid, or escape as gas ; but in 
either case they more or less accumulate about the electrodes, 
adhere to, or are absorbed by them, and alter their electrical 
relations. The direction of the current produced by polar- 
isation is opposite to that of the original one, because the 
latter has liberated electro-negative substances at the positive 
pole, and positive substances at the negative pole. 

Formation of peroxides upon the anode. — Solutions of some 
metals, when electrolysed with platinum electrodes, are spe- 
cially liable to form layers of insoluble peroxide upon the 
anodes by the action of the free oxygen of the water, liberated 
there by electrolysis. This is the case with those of the 
nitrates of lead, silver, and bismuth, the nitrate and acetate 
of manganese, and alkaline solutions of lead, cobalt and 
nickel (See ' Journal of the Chemical Society,' vol. ix., p. 307). 
In preparing the peroxides of bismuth, lead, nickel, cobalt, 
and manganese, by this method, very weak electric currents 
must be used. That of cobalt is readily prepared, and is 
permanent; its colours are magnificent, and may find an 
industrial use in the art of metallo-chromy (See pp. 242, 
260 ; Wernicke, ' Chemical News,' vol. xxii., p. 240). 

Movements in electrolytes. — As incidental effects of elec- 
trolysis I may mention the movements which take place in 
depositing liquids during the passage of the current. In 
nearly all cases the layer of liquid in contact with the anode, 
by dissolving a portion of that body, becomes specifically 
heavier than the remainder of the solution, and gradually 
sinks to the bottom ; whilst that in contact with the cathode, 
by abstraction of its metal, suffers a reverse change; i.e. it 
becomes specifically lighter and rises to the top. In this way 
a layer of heavier liquid accumulates at the bottom of the 



5 6 The A rt of Electro-Metallurgy. 

vessel, and one of less specific gravity collects at the 
surface. At the same time these two layers slowly dif- 
fuse into the intervening strata of the liquid, and thus the 
whole solution tends to become uniform ; but if this process 
of diffusion is less rapid than that of separation, there is a 
constant state of difference of chemical composition and of 
specific gravity maintained between the upper and lower 
parts of the liquid. Certain effects result from this, viz., the 
anode corrodes away very freely at its upper part, the cathode 
receives a rapid and thick deposit at its lower part ; the 
current traverses the liquid in an oblique direction down- 
wards ; the anode does not dissolve at its lower portion, 
and the upper end of the cathode receives no deposit. And 
if the liquid is very dense, and contains much free acid, each 
electrode behaves like a single metal immersed vertically in 
two liquids (see p. 84), and generates a current between its 
upper and lower parts independently of the one which comes 
from the battery ; this independent current at the anode dis- 
solves the upper portion of that body, and produces a metallic 
deposit upon its lower end, and the one at the cathode 
produces similar effects upon that metal ; and thus a deposit 
upon the upper end of a cathode may actually redissolve and 
disappear even whilst the battery current is passing. The 
most effectual way of counteracting these effects is to have 
the solution sufficiently dilute, without an excess of free acid 
or other solvent, to electrolyse it with moderate speed, and 
to stir it continually, or keep the electrodes in motion. 

Magneto-electric action. — Electro- chemical and chemico- 
electric actions, together with the principles and laws which 
regulate them, constitute the essential part of the basis of 
electro-metallurgy ; magneto-electric action is only a subsi- 
diary subject, because magneto-electric machines are merely 
one of the sources which may be employed of the electric 
current used in the art, and forms no part of the process 
itFelf. As also the principles of magneto-electric induction, 
and the construction and action of magneto- electric ma- 



Magneto-Electric Action. 57 

chines, are already described in the treatise on ' Electricity 
and Magnetism ; (pp. 70 and 280) in this Series, it is unneces- 
sary for me to say more than a few words on this part of 
the subject. 

Strictly speaking, magneto-electric action should be 
termed mechanico-electric action, because mechanical power 
is the cause and electricity the effect, and the magnetism 
acts only as an intermediate agent, by means of which the 
mechanical energy is enabled to produce or be transformed 
into electricity. The fundamental fact or principle of mag- 
neto-electric action is, wherever there is varying magnetism, 
there is a?i electric current i?iduced in an adjacent closed 
conducting circuit at right- angles to it. 

Magnetism in the vicinity of a conductor of electricity 
may be caused to vary by several means, viz. by heating or 
cooling the magnetised body (I have employed this method, 
'Proceedings of the Royal Society/ 1869, No. 108), by 
otherwise changing the strength of the magnet, by altering 
the distance of the magnet from the conductor, or by vary- 
ing their relative positions to each other. The first of these 
methods is rarely used, because it is not convenient ; but 
the others are commonly employed, and are very suitable 
and effective. The current lasts only during the increase 
or decrease of the magnetism, and is reverse in direction in 
the two cases, as indicated in the annexed figures 12 and 13. 

The magnetism acting upon the conductor may be in- 
creased or decreased, by alternately approaching the magnet 
towards and withdrawing it from the conductor, or by al- 
ternately magnetising and demagnetising a bar of soft iron, 
upon which the conductor is wound ; the latter is the 
method generally employed, and is usually effected by rotat- 
ing the iron bar and its surrounding conductor between the 
poles of a magnet. 

The alternate currents produced in th^ surrounding con- 
ductor by the magnetisation and demagnetisation of the 
iron are opposite in direction, and are caught up and thrown 



58 



'The A rt of Electro-Metallurgy. 



into one uniform course by means of a mechanical arrange- 
ment termed a commutator, which is fixed to the iron arma- 



FlG. 12. 




Increasing magnetism. 




Decreasing magnetism. 

ture and revolves with it. The current, therefore, usually 
obtained by magneto-electric action differs from that result- 
ing from a chemico-electric source, in being a succession of 
momentary streams of electricity, all flowing in the same 
direction. 

Mr. Henry Wilde, of Manchester, discovered that if the 
current from the wire of the revolving armature was made 
to flow through a coil of insulated wire surrounding a large 
bar of soft iron, a degree of magnetism many times stronger 
than that of the original magnet might be produced by re- 
volving the armature sufficiently fast ; and that by an exten- 
sion of this principle of accumulation, magnets of any degree 
of power might be obtained, limited only by the capacity of 
the iron to receive magnetism, and the amount of mechan- 
ical power expended in rotating the armatures. 

In all magneto-electric machines there exists, during their 



Thermo-Electric Action, 59 

continuance of action, incessant molecular vibrations in the 
magnet and armature, caused by the changes of magnetism, 
and in the conducting- wires, caused by the electrical waves ; 
and in consequence of these vibrations considerable heat 
is produced, which differs in amount in different machines. 
In this way a portion of the mechanical power expended is 
converted into heat instead of into electricity ; and, in ad- 
dition to this, the heat is liable to injure the insulation of the 
wires upon the armature, and damage the bearings of the 
revolving parts of the machine. 

The kinds of magneto-electric machines employed for 
electro-deposition, together with additional information of a 
more technical kind, will be illustrated and given in the 
practical division (p. 345) of this book. 

Thermo-electric actio?i. — Thermo-electric action is a much 
more secondary matter at present than magneto- electric 
induction in relation to electro-metallurgy, because it is as 
yet but little used in the art ; but its use will probably be 
largely extended, and may even supersede that of magneto- 
electric induction, because it is a much more direct conver- 
sion of heat into electric force. 

The chief fact of thermo-electric action was discovered 
by Seebeck in 1823, and is as follows : If we take two bars, 
A and B (see Fig. 14), of any two metals, especially bis- 
muth and antimony, solder their junctions, connect their 
free ends by wires, and apply heat to the soldered junction, 




Cold. — ^B Hot A.—* CoIdL 



a portion of the applied heat is absorbed and disappears, 
and an electric current is produced in its stead. 

All metals and other conductors of electricity are capable 



6o 



The Art of Electro-Metallurgy. 



of producing the current, and they are usually classed into 
thermo-electro-positive, or those in which the current pro- 
ceeds from the colder to the warmer portion, as with bismuth; 
and thermo-electro-negative, or those in which it proceeds 
in the reverse direction, as with antimony. 

In the following table by Dr. Mattheissen, the various 
metals, &c, are arranged in a series according to their relative 
degrees of thermo-electric tension : — 

Thermo-electro-positive. 



Not only solid conductors of electricity, but also liquid 
ones, are capable of yielding thermo-electric currents, and 
I have devised and employed, in several researches on the 
subject, various apparatus for the purpose (' Philosophical 
Magazine,' January 1857; ' Proceedings of the Royal Society,' 
187 1 ; Watt's Dictionary, 2nd Supplement, p. 457). 

The kinds of thermo-electric apparatus which have as yet 
been employed in electro-metallurgy are described in the 
special practical section of this book (p. 349). 



Bismuth, commercial + . 97' 


Cobalt 


22- 1 


,, pure . , 89* 


German-silver 


1 1 75 


,, crystal axial . 65* 


Mercury 


•418 


„ ,, equatorial 45' 


Lead . 


Neutral ' 


Thermo-elec 


'ro-negative. 




Copper, commercial .. -i 


Arsenic 


13-56 


Platinum ... '9 


Iron, pianoforte wire . 


i7'5 


Gold . . . .1-2 


Antimony, crystal axial 


22*6 


Antimony, pressed wire . 2 - 8 


„ equa- 




Silver, pure and hard . 3- 


torial 


26-4 


Zinc, pure, pressed wire 37 


Red phosphorus . 


297 


Copper, electro-deposited 3-8 


Tellurium . 


502- 


Antimony, commercial, 


Selenium 


807- 


pressed wire . . 6* 







Chemical Principles of Electro-Metallurgy. 

Chemico-electric relatio?is of substances. — Chemico-electric 
action often takes place in electro-metallurgical processes ; it 



Chemico-Electric Series. 



61 



continually occurs in the voltaic-batteries whilst they are in 
use ; it also takes place under several circumstances when 
metals are immersed in conducting liquids ; for instance, 
it occurs when any metal is immersed in an acid solution 
of a less positive metal than itself, as when steel or iron 
is dipped into a solution of sulphate of copper, a portion 
of the steel or iron dissolves, and produces an electric 
current. The importance of a knowledge of the relation of 
chemico-electric action to electro-metallurgy may be shewn by 
the fact, that any liquid, say the one just mentioned, in 
which the metal to be coated, say iron, is strongly electro- 
positive to the metal in solution, and with which it is in- 
tended to be coated, is usually unfit to be used for coating 
that particular metal, because if a thick coating is formed 
upon it the deposit will not adhere firmly. 

Chemico-electric series. — The following table exhibits the 
usual relative electrical positions to each other in most 
liquids of a number of the elementary substances ; the first 
substance named being the most electro-positive, and the 
last one the most electro-negative : — 



Potassium + 


Copper 


Phosphorus 


Sodium 


Silver 


Selenium 


Magnesium 


Mercury 


Iodine 


Zinc 


Platinum 


Bromine 


Iron 


Gold 


Chlorine 


Aluminium 


Hydrogen 


Nitrogen 


Lead 


Antimony 


Sulphur 


Tin 


Carbon 


Fluorine 


Bismuth 


Tellurium 


Oxygen — 



In this series every substance is usually positive to all 
those below it, and negative to those above ; consequently 
none are absolutely positive or negative, and therefore the 
series cannot strictly be divided into two classes, one con- 
sisting wholly of positive and the other of negative bodies; 
but it is usual, nevertheless, to speak of the metals, especially 
the alkali and base metals, as positive, and the metalloids as 



62 



The Art of Electro-Metallurgy. 



negative substances. Many exceptions might be shewn with 
regard to the positions of the substances in the above series, i 
because the order varies with every different liquid in which 
they may be immersed, and therefore the table is only of 
value for usual guidance. 

Electrical relations of metals in liquids. — There are several 
arrangements of immersing metals in liquids, by means of 
which electric currents are produced, and they may be classed 
as follows : i. By the immersion of two metals in one liquid. 
2. Of one metal in two liquids. 3. Of two metals in two 
liquids, &c. 

1. By the immersion of two metals in one liquid. — If we 
connect two pieces, A and B, of different kinds of metal with 
the two ends of the coil of a galvanometer C (see Fig. 15), and 

Fig. 15. 




immerse them in a conducting liquid, D, an electric current is 
generated by chemical action, and the needle is deflected ; 
and if we examine the behaviour of a number of metals thus 
in a variety of different liquids, and arrange them in series ac- 
cording to their degrees of electrical power, we find that the 
electrical positions of the metals usually agree with the order 
given in the foregoing table ; and we also find that their 
order is somewhat different in every different liquid. 

The electrical orders of metals, &c, in a number of 



Electric Relations of Metals in Liquids. 63 

different liquids are exhibited in the following series of 
tables : — 





I. Water (Fechner). 




Zinc + 


Iron 


Copper 


Lead 


Antimony 


Silver 


Tin 


Bismuth 
2. Dilute Acids (H. Davy). 


Gold- 


Potassium +. 


Iron 


Tellurium 


Barium 


Bismuth 


Gold 


Zinc-amalgam 


Antimony 


Platinum 


Zinc 


Lead 


Iridium 


Ammonium-amalgam Copper 


Rhodium 


Cadmium 


Silver 




Tin 


Palladium 





3. Equal volumes of Sulphuric Acid and Water (Pfaff). 

Zinc + Iron Gold 

Cadmium Bismuth Tellurium 

Tin Antimony Platinum 

Lead Copper Palladium — 

Tungsten Silver 

4. Very Dilute Sulphuric Acid (Marianini). 



Zinc + 

Charcoal, heated and 

quenched 
Clean Lead 
Tin 

Manganese 
Tarnished Lead 
Iron 

Magnetic Iron ore 
Brass 
Copper 
Rusty Brass 
Bismuth 
Nickel 
Charcoal 
Antimony 



Tinstone 

Native Sulphide of 

Molybdenum 
Arsenic 

Tarnished Antimony 
Silver 
Mercury 

Tarnished Arsenic 
,, Arsenical 

Silver 
Red Silver 
Galena 

Fresh Charcoal 
Copper-nickel 
Copper-glance 
Arsenical Cobalt 



Black Tellurium 

Copper pyrites 

Platinum 

Gold 

Auriferous native Tel- 
lurium 

Cubical Iron pyrites 

Graphite 

Arsenical pyrites 

Magnetic , , 

Amorphous Iron py- 
rites 

Peroxide of Manganese 

Old Charcoal - 



6 4 



The Art of Electro-Metallurgy. 



5. Hydrochloric Acid (Faraday). 



Zinc + 


Iron 


Silver 


Cadmium 
Tin 


Copper 
Bismuth 


Antimony 


Lead 


Nickel 





1 volume of Nitric Acid a?id 7 volumes of Water (Faraday). 

Zinc + Iron Copper 

Cadmium Nickel Silver — 

Lead Bismuth 

Tin Antimony 

7. Nitric Acid, sp.gr. 1*48 (Faraday). 

Cadmium + Iron Silver 

Zinc Bismuth Nickel — 

Lead Copper 

Tin Antimony 

8. Concentrated Nitric Acid (De la Rive). 



Tin + 


Copper Silver 


Zinc 


Lead Peroxide of Iron 


Iron 


Mercury 


9. Pure Dilute 


Hydrofluoric Acid of 10 per cent. (Gore). 


Aluminium + 


Lead Bismuth 


Zinc 


Silicon Copper 


Magnesium 


Iron Silver 


Thallium 


Nickel Gold 


Cadmium 


Cobalt Gas-carbon 


Tin 


Antimony Platinum — 


10. Pure Dilute 


Hydrofluoric Acid of '28 per cent. (Gore). 


Zinc + 


Nickel Gas-carbon 


Magnesium 


Cobalt Platinum 


Aluminium 


Antimony Rhodium 


Thallium 


Bismuth Palladium 


Indium 


Mercury Tellurium 


Cadmium 


Silver Osmi-iridium 


Tin 


Copper Gold 


Lead 


Arsenic Iridium — 


Silicon 


Osmium 


Iron 


Ruthenium 



CJiemico-Electric Series. 6$ 

II. Aqueous Potash or Soda (H. Davy). 
Alkali-metals + Copper Gold 



Zinc 


Iron 


Platinum — 


Tin 


Silver 




Lead 


Palladium 





12. Solution cf Potash or Soda, strong or weak (Faraday). 

Zinc + Lead Nickel 

Tin Bismuth Silver — 

Cadmium Iron 

Antimony Copper 

13. Solution of Potash or Soda, sp. gr. 1*33 (Pfaff). 

Tin + Copper Steel 

Zinc Gold Silver — 

Antimony Platinum 

Lead Bismuth 

14. Aqueous Ammonia, sp. gr. '95 (Pfaff). 

Zinc + Lead * Copper — 

Tin Silver 

[5. 1 part of Cyanide of Potasshwi in 8 parts of Water (Poggendorff). 

Amalgamated Zinc + Nickel Iron 

Zinc Antimony Platinum 

Copper Lead Cast-iron 

Cadmium Mercury Coke — 

Tin Palladium 

Silver Bismuth 

16. Dilute Yellow Sulphide of Potassium (Faraday). 
Zinc + Silver Bismuth 
Copper Lead Iron — 
Cadmium Antimony 

Tin Nickel 

17. Dilute Hydrosulphate of Potassium (H. Davy). 

Zinc + Bismuth Gold 

Tin Silver Charcoal — 

Copper Platinum 

Iron Palladium 

F 



66 



The Art of Electro- Metallurgy. 



iS. Colourless Solution of Sulphide of Potassium (Faraday). 



Cadmium + 
Zinc 


Antimony- 
Silver 


Nickel 
Iron — 


Copper 
Tin 


Lead 
Bismuth 





19. Solution of Sal-ammoniac (Poggendorff). 

Zinc + 

Cadmium 

Manganese 

Lead 

Tin 

Iron 

Steel 

Uranium 

Brass 



Magnetic Iron 


Copper pyrites 


German-silver 


Tellurium 


Cobalt 


Gold 


Bismuth 


Galena 


Antimony 


Coke 


Arsenic 


Platinum 


Chromium 


Plumbago 


Silver 


Peroxide of Maa 


Mercury 


ganese — 



20. Solution of Common Salt (Fechner). 



Zinc + 
Lead 
Tin 
Iron 



Antimony 
Bismuth 
Copper 
Silver 



Gold 
Platinum 



2 1 . Fused Boracic Acid ( Gore) . 

Iron + Platinum Silver 

Silicon Gold 

Carbon Copper 



22. Fused Phosphoric Acid (Gore). 



Zinc 
Iron 



Copper 
Silver 



Platinum 



23. Fused Potassic Hydrate (Gore). 



Silicon + 

Aluminium 

Zinc 



Iron 
Lead 
Carbon 



Platinum 
Silver — 



Chemico-Electric Relations. 6? 

24. Fused Potassic Carbonate (Gore). 



Silicon + 

Iron 

Zinc 


Carbon 
Copper 
Silver 


Platinum 


25. 


Fused Potassic Chloride (Gore). 


Aluminium 4- Iron 
Zinc Copper 


Silver 
Platinum 


26. 


Fused Potassic Fluoride (Gore). 


Palladium + Platinum 
Gold 


Iridium - 



27. Fused Amnionic Nitrate (Gore-). 

Magnesium + Silver Silicon 

Zinc Tin Carbon 

Lead Aluminium Platinum — 

Copper Iron 

Additional information respecting the chemico-electric 
relations of metals in aqueous solutions will be found scat- 
tered throughout the book under the headings of the respec- 
tive metals, and for additional tables of the electrical relations 
of metals in fused substances see 'Philosophical Magazine, 5 
June 1864 ; 'Chemical News,' vol. ix., p. 266. 

The earliest kinds of voltaic batteries were composed of 
two metals immersed in one liquid, and from the outset zinc 
appears to have been almost the only metal employed as the 
positive element. The currents obtained from them were 
stronger in proportion as the two metals were further asunder 
in the general series (p. 61) ; thus they were stronger 
when silver was substituted for copper, and platinum or 
carbon for silver, as the negative element ; and they were 
obtained still stronger by selecting from the special series 
the most suitable liquid in which to immerse them. It was 
practically by selecting metals and liquids in accordance 

f 2 



68 The A rt of Electro- Metallu rgy. 

with these series, and especially those which were the most 
durable and least expensive, that the earlier kinds of bat- 
teries were invented. No powerful battery is composed of 
two metals which lie close together in the series, such for 
instance as zinc with cadmium, tin, lead, or iron in dilute 
sulphuric acid. The chief batteries of this class, i.e. of two 
metals immersed in one liquid, are the old zinc and copper 
one, Cruickshank's, Wollaston's, and Smee's. 

The value of cyanide solutions, for the purposes of 
electro-plating, is also largely dependent upon the electrical 
relations of the baser metals to gold and silver in such 
liquids. If we refer to Tables i to 12 (pp. 63, 64) we may 
perceive that in aqueous acids the baser metals are high up 
in the lists, and more electro-positive, and gold, silver, and 
copper either lower or a long way down ; but in aqueous 
cyanide of potassium (Table 15), or sulphide of potassium 
(Tables 16, 17, 18), each of them strongly alkaline liquids, 
copper and silver are much higher up, and iron much lower 
down; and in consequence of this the anode of nobler 
metal is more easily dissolved, and a receiving surface of iron 
is less corroded. 

The electrical relations of metals and carbon, &c, in 
fused substances have not yet found to any notable extent 
similar practical applications, but it is not improbable that 
some will be found, because they hold out a prospect of ob- 
taining electric currents by means of the combustion of coke. 
'The discovery of some suitable fused salt or mixture, in which 
carbon is highly electro-positive at a high temperature to iron, 
nickel, or other infusible and also in other respects suitable 
conductor, would probably prove a cheap and powerful source 
of electricity ; cheap, because of the low chemico-electric 
equivalent of carbon in relation to that of zinc, and the low- 
price of coke and gas-graphite ; and powerful, because of the 
intense affinity of carbon for oxygen at high temperatures, 
sufficient indeed to set the alkali metals free from their 
oxides. The nearest approach to this object in these expert 



Chemico-Electric Relations. 69 

merits' (in experiments with metals in fused substances) 
* was obtained with carbon and nickel, immersed in a fused 
mixture of soda, lime, and silica, i.e. in a species of glass ' 
(' Philosophical Magazine,' June 1864 ; ' Chemical News,' 
vol. ix., 1864, p. 266). 

2. By immersion of one metal in two liquids. — If two 
pieces of the same metal are immersed in two different con- 
ducting liquids, the liquids being in contact with each other 
through the medium of a porous partition or other suitable 
means, such as placing the two liquids in the two legs of a 
bent glass tube, &c, an electric current is produced. A large 
number of instances of currents generated by means of this 
arrangement are described in Gmelin's ' Handbook of Che- 
mistry,' vol. i., p. 397, and one or two voltaic batteries have 
been constructed according to it, but have not come intc 
extensive use. 

3. By immersion of two metals in two liquids. — Any two 
metals immersed in any two conducting liquids which are in 
mutual contact will also produce an electric current, and 
the strongest voltaic currents are obtained by means of this 
arrangement, because there is not only an electrical and 
chemical difference of metal, but also of liquid. Dani ell's, 
Bunsen's, Grove's, and many other batteries, are of this kind. 

The particular liquid in which the most positive metal 
is the most positive is not necessarily the same liquid as that 
in which the most negative metal is the most negative, and 
therefore a one-liquid battery does not give the strongest 
current ; but this arrangement of two metals and two liquids 
enables us to combine the advantages of both liquids, and 
thus obtain a more powerful current. 

A very large number of batteries have been devised and 
constructed in accordance with one or other of these arrange- 
ments, and many are in practical use. The particular kinds 
of them which have been employed for the purposes of 
electro-metallurgy will be described in the practical division 
of this book. 



fo The A rt of Electro-Metallurgy. 

Voltaic currents. — As the origin of the currents in voltaic 
batteries, the terms tension, potential, intensity of current, 
quantity of current, electro-motive force, &c, are fully ex- 
plained in another book of this series, viz. the ' Treatise on 
Electricity and Magnetism,' by Fleeming Jenkin, F.R.S., I 
shall say no more than is requisite on those points, but refer 
the reader to that treatise for fuller information. 

The electrical relations of metals in liquids are the chief 
source of all voltaic currents, and the main fact upon which 
the action of all voltaic batteries depends. If two different 
metals are immersed in a conducting liquid, or in two such 
liquids, the liquids being in mutual contact, and the metals 
united by a wire, a constant state of electric difference is 
produced in them by their mutual contact, and by a differ- 
ence of chemical action of the liquid or liquids upon them ; 
and this is the commencement of all voltaic action, and the 
origin of electro-motive force. The particular kind of chemical 
action which is the main source of the current in nearly all 
such batteries is the union of the zinc with the oxygen of 
the liquid in contact with it. 

Electro-motive force. — The electro-motive force, or strength 
of the current to overcome resistance, depends upon the 
degree of difference of strength of chemical affinity of the 
two metals for the electro-negative constituents of the liquid. 
The farther asunder, therefore, the two metals are in the 
chemico-electric series (p. 61), the greater usually is the 
difference of intensity of chemical action of ordinary acid 
liquids upon them, and the stronger also is the electro-motive 
force. This general truth may be easily verified by con- 
necting pieces of platinum and copper with a galvanometer, 
and immersing their ends in dilute nitric acid whilst watching 
the needle ; then make a similar experiment with copper and 
zinc in dilute sulphuric acid ; also with zinc and magnesium 
in extremely dilute sulphuric acid ; and it will be found that 
in each case the current proceeds from the metal which is 
most acted upon, through the liquid to the other metal. The 



Electro- Motive Force. 7 1 

electro-motive force evidently depends also upon a more 
fundamental point, which as yet has been but comparatively 
little studied, viz. upon the kind of chemical affinity exer- 
cised between the positive metal and the negative consti- 
tuents of the liquid ; for instance, copper is powerfully 
corroded by nitric acid, but although the intensity of chemi- 
cal attraction is great in this case, the electro-motive force 
generated is comparatively feeble. I have made some 
experiments upon this point. The ordinary unit of electro- 
motive force employed in this country is termed a ' volt ' 
(see Jenkin's 'Treatise on Electricity and Magnetism,' 
p. 159 ; also Appendix, p. 387 of this work). 

Potential and tension. — Previous to the completion of 
the circuit and formation of an unimpeded current, the free 
ends of the polar wires attached to the two metals are 
charged with the two kinds of electricity in an accumulated 
or free static condition, and are in a state of electric potential \ 
i.e. possessing a capability of doing electric work. These 
accumulated electricities in the wires may be detected by 
means of a very delicate electroscope. The free electricities 
are also in a state of tension, constantly tending to escape 
and unite ; and their degrees of tension may be measured 
by means of an electrometer ; the degree of tension, how- 
ever, in a single voltaic cell is extremely small, and has been 
estimated to be about ten million times less than that of an 
ordinary frictional electric machine. 

Current ; strength of current. — The continual union ot 
the two electricities through the connecting wire, or other 
conductor, constitutes an electric current. Any given voltaic 
battery can only yield a given maximum strength of current. 
The strength is the amount or quantity of electric force which 
flows through any given section of the circuit in a given period 
of time. It depends upon two conditions, viz. the electro- 
motive force of the battery, and the total amount of resist- 
ance in the circuit. The strength of the current is equal 
to the electro-motive force divided by the resistance ; this 



72 The Art of Electro- Metallurgy. 

is known as Ohm's law ; it is directly proportional to the 
electro-motive force, and inversely proportional to the resist- 
ance ; if the resistance remains the same, and the electro- 
motive force varies, the strength is directly proportional 
to the electro-motive force; and if the electro-motive 
force remains the same, and the resistance varies, it is in- 
versely proportional to the whole of the resistance in the 
circuit (see Appendix, p. 387). 

Resistance; 'intensity' of current. — The total resistance 
in the circuit is usually divided into internal, or that in the 
battery itself ; and external, or that in the connecting wires 
and other portions of the circuit outside the battery. If the 
external resistance is much less than that of one cell, as 
when the poles of a single voltaic cell are connected by a 
short and thick copper wire, any addition to the number of 
cells in the battery will produce no perceptible increase of 
current, because by that addition we augment the internal 
resistance as fast as we increase the electro-motive power. 
But if the external resistance is much greater than the resist- 
ance in the battery, any addition to the number of cells 
will produce a nearly proportionate increase in the quantity 
or strength of the current, because we then increase the 
electro-motive force much faster than we augment the total 
amount of resistance. 

A current which is but little diminished in amount by the 
introduction of a given external resistance is, in common 
language, said to possess great ' intensity ' ; but the differ- 
ence of effect produced by means of a current from one cell 
and that from many, does not arise from any real difference 
in the nature of the currents in the two cases, but from the 
difference of proportion of external to internal resistance. 
No difference has hitherto been recognised in any two cur- 
rents of equal quantity per minute, obtained from different 
voltaic sources. 

Measurement of curre?it — The quantity of electricity 
circulating may be measured by the amount of electric work 



Measurement of Current. 



73 



performed, and the strength of the current by the amount of 
such work done in a given period of time. 

The instruments usually employed for this purpose are 
either a galvanometer or a voltameter. The construction, 
action, and mode of using a galvanometer are already fully 
described in the ' Treatise on Electricity and Magnetism ' of 
this series, p. 187. One suitable for 
use in electrolytic experiments should 
offer but little resistance to the passage 
of the current, and what is termed ' a 
tangent ' one may be conveniently em- 
ployed, because the magnetic action of 
the current upon the needle is then 
much less powerful. 

Voltameters are of different kinds ; 
that originally employed by Faraday 
contained a mixture of sulphuric acid 
and water as the electrolyte. A water 
voltameter is shown in the annexed 
sketch, Fig. 16. Two graduated glass 
tubes, A and B, open at the bottom, and provided with 
stop-cocks at their upper ends, are inverted over two large 
plates of platinum, C and D, which are connected to the 
binding screws, by means of wires beneath. The outer glass 
jar is nearly filled with a previously-cooled mixture of about 
3 J or 4 measures of distilled water and 1 measure of pure sul- 
phuric acid, the acid being added to the water, not the reverse. 
On passing the current to be measured from C to D, oxygen 
collects in C and hydrogen in D, and the quantity of elec- 
tricity passed varies directly as the amount of gas evolved. 

In this form of voltameter a little error arises in conse- 
quence of a small portion of the gas being dissolved in the 
water, and also from unequal pressure of the liquid upon 
different quantities of gas ; if also the current to be measured 
is one of low electro-motive force, its amount is largely 
diminished by the resistance in the voltameter itself. 




74 The A rt of Electro-Metallurgy. 

An arrangement which offers less conduction resistance, 
and which is very convenient, consists in passing the current 
through two large electrodes (the cathode being a thin one) 
of pure and clean sheet copper, immersed in a nearly satu- 
rated solution of sulphate of copper, to which has been sub- 
sequently added about one-sixth its bulk of pure dilute sul- 
phuric acid, and carefully weighing the cathode before and 
after the experiment. Each atomic weight, 63-5 parts in 
grains, may, as copper is a dyad (see p. 41), be said to 
represent two equivalents of electricity. 

Amounts of electricity produced by different metals. — As 
the proportionate number of atomic weights of a substance 
dissolved or deposited by electrolysis depends upon the 
'valency' of the elements (see p. 41), so in like manner 
does the quantity of the current generated in a voltaic 
battery depend upon the same condition. Thus one atomic 
weight (say in grains) of a monad element will produce one 
equivalent of electricity, a dyad two, a triad three, a tetrad 
four, &c. Whilst it is the degree of intensity of chemical 
attraction of the positive metal by the negative element of 
the liquid in the battery which determines the electromotive 
force of the current, it is the qua?itity of the substances 
attracted which determines its amount. 

Relatio?i of the quantity of chemical action in the lattery to 
that i?i the depositing vessel. — The relations of the electric 
current, both to the quality and quantity of electrolytic effect, 
have already been described (p. 35 to 45); and those re- 
lations are the same whether the current producing the elec- 
trolysis is generated in the electrolytic vessels themselves, 
or in separate batteries, or other electro-motors. And, as 
a chemico- electric equivalent of metal dissolved in the 
battery generates an equivalent of electricity, and an 
equivalent of electricity deposits an equivalent of metal in 
the deposit-cell (pp. 42, 44), we may now say that, usually, 
for each chemical equivalent of substances dissolved, set free, or 
formed, in each cell of the battery, a chemical equivalent of other 



Definite Electro- Chemical A ction. 7 5 

substance is dissolved, set free or formed, in each depositing vessel, 
in the same circuit ; and that this equivalency of action 
throughout the circuit is due to the fact that each chemical 
equivalent of any substance has associated with it an equal 
amount of electricity. This is the law of definite electro- 
chemical action. 

Faraday established that law. He found that ' if the 
current of a battery be passed through a voltameter contain- 
ing dilute sulphuric acid and platinum electrodes, and thence 
by means of a platinum wire entering the upper end, and con- 
veying positive electricity into a glass tube containing fused 
protochloride of tin, and having inserted into its lower end 
a platinum wire, which serves as the negative electrode, 
then for every 9 parts of water decomposed in the volta- 
meter 58-53 parts of tin are deposited on the last-mentioned 
wire ' (the atomic weight of tin is 118). \ When fused chloride, 
iodide, oxide, and borate of lead were treated in a similar 
manner, the quantity of lead obtained was too small in pro- 
portion to the water decomposed, viz. to 9 parts of water, 
1 00 -8, 89*, 93*2, and 101*3 l ea A whereas the atomic weight 
of lead is 207' (or 103-5 x 2 ? ^ ea( ^ being a dyad). 'The cause 
of the deficiency is, probably, that a portion of the precipi- 
tated lead was redissolved by the anion ; a kind of circum- 
stance which occasionally happens. When two silver wires 
are introduced as electrodes into fused chloride of silver, the 
weight of the positive electrode diminishes almost exactly 
108-1 parts for every 9 parts of water decomposed in the 
voltameter, whilst that of the negative electrode increases by 
the same quantity. Chloride and iodide of lead treated 
in the same manner, lead being used as the positive electrode, 
gave 10 1 -5, and 103*5 l ea -d for every 9 parts of water.' 

According to Quincke, the force tending to separate the 
constituents of an electrolyte is proportional to the density 
of the current, i.e. to the strength of the current per unit of 
sectional area of the liquid ; it also increases with the electro- 
motive force of the current employed, and is inversely pro- 



j 6 The Art of Electro-Metallurgy. 

portional to the length, but independent of the cross-section 
and of the conductivity of the liquid, if the resistance of the 
remainder of the circuit is small in comparison with that 
of the electrolyte (' Journal of the Chemical Society/ vol. x., 
p. 208). 



PRACTICAL DIVISION. 
SECTION A. 



General methods of deposit 'i?ig metals. — There are various 
methods which either have been or are still employed in 
depositing metals from their solutions for practical purposes, 
and they may be classed as follows — 1st. By immersi?ig one 
metal in one liquid, as, for instance, by immersing steel or iron 
in a slightly-acidulated solution of sulphate of copper. 2nd. 
By immersing two metals in one liquid, as by immersing the 
article to be coated in contact with zinc or other sufficiently 
positive metal in the particular metallic solution. 3rd. By 
immersing one metal in two liquids, as, for instance, if a deep 
glass vessel be half filled with a saturated aqueous solution 
of cupric sulphate, the vessel be then nearly filled with water 
containing a small quantity of sulphuric acid, poured in 
quietly so as not to mix with the copper solution, and a 
bright rod of copper, as deep as the vessel, be allowed to 
remain in a vertical position in the liquid during twenty-four 
hours without disturbance ; the upper half of the rod will 
slowly corrode and dissolve, whilst the lower half will receive 
a deposit of copper. 4th. By immersing two metals in two 
liquids, as in the ordinary c single cell ' electrotype appa- 
ratus. 5th. By the separate current plan, as when a voltaic 
battery, magneto-machine, or thermo-electric pile is em- 
ployed with a separate depositing vessel. 

Under each of these classes will be mentioned a number 
of experiments made by the author, and it is desirable that 




Methods of Electro-Deposition. J 7 

the student should repeat a few. of them, in order to fix the 
general principles more firmly in his memory. 

Method No. 1. — Deposition by immersing one metal in one 
liquid (see Fig. 17). With aqueous solutions of the following 
salts I obtained the effects mentioned. In Fig. 17. 

hydrochlorate of terchloride of antimony (a 
solution of terchloride of antimony in hy- 
drochloric acid), as prepared for pharma- 
ceutical purposes, zinc, bismuth, tin, lead, 
brass, and german -silver became coated 
with antimony ; whilst antimony, nickel, 
silver, gold, and platinum did not. 

Chloride of bismuth. — Zinc, tin, lead 
and iron deposited the bismuth upon 
themselves, whilst antimony, bismuth, 
copper, brass, german- silver, gold, and platinum did not. 

Tetrachloride of platinum. — Platinum was deposited from 
a solution of its chloride by arsenic, antimony, tellurium, 
bismuth, zinc, cadmium, tin, lead, iron, cobalt, nickel, 
copper, brass, german-silver, mercury, and silver ; but not 
by gold or platinum. 

Gold solutions. — From an acid solution of terchloride 
of gold, the base metals, likewise mercury, silver, plati- 
num, and palladium, deposited gold in the metallic 
state ; arsenic rapidly deposited gold in this solution ; 
antimony, tellurium, and bismuth became gilded ; zinc, 
cadmium, lead, iron, cobalt, mercury, silver, platinum, and 
palladium deposited the gold. In a solution of the double 
cyanide of gold and potassium, zinc quickly became gilded, 
and copper, brass, and german-silver slowly, whilst antimony, 
bismuth, tin, lead, iron, nickel, silver, gold, and platinum 
did not. 

Silver solutions. — The following metals, viz. manganese, 
arsenic, antimony, bismuth, zinc, cadmium, tin, lead, iron, 
copper, and mercury deposited silver from its solutions in 
the metallic state. An aqueous solution of nitrate of silver 



78 The A rt of Electro-Metallurgy. 

yielded its metal to manganese, arsenic, antimony, bismuth, \ 
zinc, tin, lead, iron, nickel, copper, brass, and german-silver ; 
but not to silver, sold, or platinum ; lead and tin deposited , 
the silver most quickly ; then followed the other metals in 
this order : cadmium, zinc, copper, bismuth, antimony, 
arsenic, mercury. Arsenic deposited silver from the alcoholic 
solution of nitrate of silver \ antimony received a coating of 
silver either in the aqueous sulphate or alcoholic nitrate ; 
bismuth deposed silver from the alcoholic nitrate, but not 
from the aqueous sulphate ; zinc received a silver deposit in 
the alcoholic nitrate ; tin became silvered in the alcoholic 
nitrate, but more quickly in the aqueous sulphate ; iron 
deposited silver from the sulphate of silver, but not from the 
alcoholic nitrate ; copper deposited it from the aqueous sul- 
phate or alcoholic nitrate ; brass and the alloys of silver, with 
zinc, tin, or lead, deposited silver from silver solutions com- 
pletely. In a solution of the double cyanide of silver and potas- 
sium (the ordinary silver-plating liquid), zinc, lead, and 
copper became silvered ; also brass and german-silver, but 
more slowly ; whilst antimony, bismuth, tin, iron, nickel, 
silver, gold, and platinum did not. 

Mercurous salts. — Solutions of mercurous salts have their 
metal deposited by arsenic, antimony, bismuth, zinc, cad- 
mium, tin, lead, iron, copper, and brass, also by the alloys 
of silver with zinc, tin, lead, or copper. 

Nitrate of mercury. — A solution of nitrate of mercury 
yielded its metal to bismuth, zinc, cadmium, lead, iron, or 
copper, and if acidulated with nitric acid, to antimony also, 
but not to silver, gold, or platinum. 

Acetate of mercury. — Iron deposited mercury from a 
solution of this salt. 

Sulphate of copper. — In a solution of sulphate of copper, 
zinc, tin, lead, and iron became coated with copper, whilst 
antimony, bismuth, nickel, copper, silver, gold, and platinum 
did not. 

Cupric chloride. — In a solution of chloride of copper, 



Methods of Electro-Deposition. 79 

bismuth, zinc, tin, lead, and iron received a copper deposit ; 
whilst antimony, nickel, copper, silver, gold, and platinum 
did not. 

JVitrate of copper. — In a solution of nitrate of copper, 
zinc, tin, lead, and iron became coated ; whilst antimony, 
bismuth, nickel, copper, silver, gold, and platinum did not. 

Ammonio-chlorides of copper. — With a solution of sub- 
chloride of copper in liquid ammonia, or of black oxide of 
copper in a solution of sal-ammoniac, zinc received a deposit ; 
whilst antimony, bismuth, tin, lead, iron, nickel, copper, 
silver, gold, or platinum did not. 

Ferrous sulphate. — ' Zinc,' as Fischer says, ' immersed in 
a perfectly neutral solution of ferrous sulphate (protosulphate 
of iron), contained in a stoppered bottle, throws down me- 
tallic iron, which is deposited partly on the zinc ; ' but, in my 
experience, with this solution neither antimony, bismuth, tin, 
lead, iron, nickel, copper, brass, german-silver, silver, gold, 
or platinum received any metallic deposit. 

Hyponitrite, nitrate, or acetate of lead. — In a solution of 
Jiyponitrite, nitrate, or acetate of lead, zinc received a coating 
of lead ; whilst antimony, bismuth, tin, lead, iron, nickel, 
copper, brass, german-silver, silver, gold, and platinum re- 
ceived no deposit. 

Stannous chloride. — In a solution of stannous chloride, 
zinc and lead become tinned ; whilst antimony, bismuth, tin, 
iron, nickel, copper, brass, german-silver, silver, gold, and 
platinum receive no deposit. 

Sulphate, chloride, nitrate, or acetate of zinc. — In a solution 
of either sulphate, chloride, nitrate, or acetate of zinc, neither 
antimony, bismuth, zinc, tin, lead, iron, nickel, copper, brass, 
german-silver, silver, gold, or platinum became coated with 
zinc. 

Observations upon class of instances No. 1. — In reviewing 
all these instances, we may make the following observations: 
1st, that various metals by mere immersion in solutions of 
other metals, at the ordinary temperature of the atmosphere, 



80 The A rt of Electro-Metallurgy. 

sometimes become coated with a deposit of metal, and some- 
times not ; 2nd, that a metal rarely becomes coated by mere 
immersion in a solution of the same metal ; for instance, | 
zinc does not become coated with zinc in a solution of sul 
phate of zinc (see p. 79), copper with copper in a solution of 
its sulphate, gold with gold in its chloride, &c. ; 3rd, that the 
baser metals, especially zinc, cadmium, tin, lead, and iron, 
become coated more frequently than the noble metals, 
especially gold and platinum ; 4th, that solutions of base 
metals, especially of zinc and iron, yield their metal less 
frequently than those of the noble metals, especially those of 
gold and platinum ; 5th, that of all the ordinary metals men= 
tioned in the foregoing instances, zinc deposits metal from the 
greatest number of solutions, and appears to have the strong- 
est depositing power ; 6th, that the coherent and adhesive 
deposits obtained are in all cases exceedingly thin ; and 7th, 
that oftentimes the deposited metal, whatever its kind may 
be, has the appearance of a black or dark- coloured powder on 
its surface, especially when it has been deposited very rapidly ; 
and that sometimes it exhibits its ordinary colour and 
appearance, especially if its outer portion is rubbed off. 

By the simple immersion process a thin coating only of [ 
metal is usually obtained, and even that is imperfect, because \ 
the surface to be coated and the coating of metal act elec- 
trically as two different substances, the former being electro- 
positive and the latter electro-negative. In consequence of 
this electrical difference there is set up a voltaic action at 
minute points all over the surface ; this action is not per- 
ceptible at first because it is of microscopic minuteness, but 
it gradually spreads from those points all over the surface, 
and causes the metal beneath the coating to dissolve, and 
the deposit to become loose and full of spots. 

It is, however, possible to coat a metal perfectly with 
another metal by means of simple immersion by adopting 
the following rule, now I think for the first time published. 
Take an electro-positive metal. A (say copper), dip it into a 



Methods of Electro-Deposition. 



Si 



solution of a less positive metal, B (say mercury), its surface 
then dissolves and a film of B is deposited upon it. Now 
dip it into a solution of a third and still less positive metal, 
C (say gold) ; the film of B and also any non-coated particles 
of A then dissolve, and a film of C is deposited in their 
stead. Now re-dip the metal A into the solution of B, and 
any still non-coated particles of it are dissolved, and deposit 
B in their place ; then dip again into the solution of C, and 
a similar effect takes place as before. By thus alternately 
dipping the metal A, into the solutions of B and C, the num- 
ber of its non-coated particles becomes less and less, until 
every one is coated with the metal C (see p. 128). The 
rule is applicable to various metals to which it has not yet 
been applied ; and its application offers an opening for new 
inventions. 

To the simple immersion mode of depositing, belongs 
the process of tinning brass articles (wash tinning), by boil- 
ing them in water containing a salt of tin 
and bitartrate of potash ; the process of 
silvering brass nails, buttons, hooks and 
eyes, buckles, &c, by rubbing them with 
any of the well-known silvering composi- 
tions moistened with water; also the water- 
gilding process (see pp. 265, 152, 127). 

Method No. 2. Deposition by two 
metals and one liquid or * by simple contact 
process ' (see Fig. 18). The following in- 
stances belong to the class of deposition 
by two metals and one liquid, the two 
metals being either in mutual contact 
(touching each other either above or 
beneath the surface of the liquid), or connected together by 
a wire. 

In chloride of antimony. — On immersing a piece of anti- 
mony in contact with a piece of zinc in a solution of the 
ordinary chloride of antimony, it received a coating of anti- 

G 




8 2 The A rt of Electro-Metallurgy. 

mony, and on immersing a piece of platinum in contact with 
a piece of tin in this liquid, it received a deposit of antimony ; 
but on immersing a piece of antimony in contact with a 
piece of platinum, or a piece of platinum in contact with a 
piece of silver in this liquid, it received no metallic deposit. 

Chloride of bismuth. — In a solution of this salt, brass in 
contact with a piece of zinc, copper in contact with tin, or 
german-silver with iron, received a deposit of bismuth ; but 
brass in contact with a piece of gold, gold in contact with 
silver, or german-silver with platinum, received no deposit. 

Tetrachloride of platinum. — In a solution of this salt, 
platinum in contact with zinc became coated with platinum, 
but in contact with gold it received no such coating. 

Nitrate of silver. — In a solution of argentic nitrate, gold 
in contact with zinc received a deposit of silver, but in 
contact with platinum it did not. 

Nitrate of 7nercury. — In a solution of this salt, silver in 
contact with either zinc or iron, or platinum in contact with 
copper, received a metallic deposit; but platinum in contact 
with silver did not. 

Sulphate of copper. — In a solution of cupric sulphate, 
brass in contact with zinc, or tin, german-silver, silver, or 
platinum, in contact with iron, received a deposit of copper ; 
whilst silver in contact with antimony, or platinum in contact 
with brass, received no deposit. 

Oxide of copper in ammonia. — In a solution of oxide of 
copper in ammonia, platinum in contact with zinc received 
a deposit ; but silver in contact with iron did not. 

Chloride of nickel and ammonium. — In a solution of the 
double chloride of nickel and ammonium, copper in contact 
with zinc received a deposit of nickel, but in contact with 
silver it did not receive such a deposit. 

Protosulphate of iron. — With a saturated solution of this 
3 .It, platinum in contact with zinc received a deposit of iron ; 
but in contact with copper it received no metallic deposit. 

Hyponitrite of lead. — With a solution of hyponitrite of 



Methods of Electro-Deposition. 83 

lead, either tin, copper, or brass, in contact with a piece of 
zinc, received a deposit of lead ; but copper in contact with 
tin or lead, or brass with platinum, received no deposit. 

Nitrate of lead. — With a solution of plumbic nitrate, 
either copper, brass, or silver, in contact with zinc, received 
a coating of lead ; but copper in contact with iron, brass 
with tin, or silver with copper, received no such coating. 

Stannous chloride. — With a solution of this salt, either 
antimony, tin, or copper, immersed in contact with zinc or 
lead, received a coating of tin ; but antimony in contact 
with tin, tin with silver, copper with iron, or either gold or 
platinum with copper, did not receive a deposit. 

Sulphate, chloride, or nitrate of zinc. — With a solution of 
either sulphate, chloride, or nitrate of zinc, no metal of any 
pair of metals, selected from amongst the following, received 
a deposit of zinc :• antimony, bismuth, zinc, tin, lead, iron, 
nickel, copper, mercury, silver, gold, platinum, or palladium. 

Observations upon class of instances No. 2. — The following 
general observations may be made upon the foregoing facts : 
firstly, that in some instances deposition does, and in others it 
does not, occur ; secondly, that a metal will not usually cause 
another metal to be coated by this method, unless it can coat 
itself in the same liquid by simple immersion — -for instance, 
zinc cannot coat itself with zinc in solutions of that metal, 
neither can it usually cause other metals to become coated 
with that metal in those solutions (see above) ; copper can- 
not usually coat itself with zinc in a. solution of sulphate of 
zinc, or with tin in a solution of chloride of tin, neither does 
it usually cause silver, gold, or other metal, to become coated 
with zinc or tin in those liquids (see Raoult's experiments, 
pp. 268, 273, 276); thirdly, that one of the two metals which 
receives a deposit by this method, derives its power of receiv- 
ing it by virtue of its contact with the other metal ; fourthly, 
that any metal which has the power of coating itself by 
simple immersion in a given liquid can, by this method, cause 
other metals which do not coat themselves by simple immer- 

G 2 



84 The A rt of Electro-Metallurgy. 

sion in that liquid, to become coated ; for instance, zinc, tin, 
and iron, coat themselves with copper, by simple immersion 
in a solution of sulphate of copper, but silver, gold, and 
platinum do not ; but if either of the former metals be con- 
nected with either of the latter, the two being immersed toge- 
ther in that liquid, the latter metals, as well as the former, 
will become coated with copper ; fifthly, that base metals, and 
especially zinc, have generally the power of causing other 
metals to become coated by this method, whilst the noble 
metals, and especially gold and platinum, rarely possess this 
power; sixthly, that by this method, metal is deposited much 
more frequently from solutions of the noble metals, than 
from those of the base ones ; and, finally, that thick de- 
posits of metal may be obtained by this method, provided the 
action is continued sufficiently long and the liquid properly 
renewed. 

Method No. 3. — Deposition by one metal and two liquids 
(see Figs. 19, 20). — The following instances belong to de- 
position by the immersion of one metal in two liquids, 
separated by a porous diaphragm, the metal being either in 
two pieces, connected together by a wire or wires, or in one 
piece, and bent so as to dip into both liquids, or the dia- 
phragm may be dispensed with, as already explained, by 
pouring the lighter liquid carefully above the other, and 
placing the piece of metal vertically in the two liquids 
(see Fig. 19). 

Antimony in chloride of antimony. — Two pieces of anti- 
mony, connected together by a wire or wires, were immersed, 
one in dilute nitric acid, and the other in a solution of chloride 
of antimony : the piece in the dilute acid dissolved, whilst 
that in the chloride solution received a metallic deposit. 

Iron in chloride of antimony. — With iron in dilute sul- 
phuric acid on one side, and in a solution of chloride of 
antimony on the other, the end in the metallic solution 
received a deposit of antimony, whilst that in the dilute acid 
dissolved. 



Methods of Electro-Deposition. 



85 



Antimony in chloride of bismuth. — Two pieces of anti- 
mony were immersed in the previous manner, one in hydro- 

Fig. 19. Fig. 20. 





chloric acid, and the other in a solution of chloride of bis- 
muth ; that in the acid dissolved, and the other received a 
coating of bismuth. 

Bismuth in chloride of bismuth. — With bismuth in hydro- 
chloric acid on one side, and in a solution of chloride of 
bismuth on the other, a free deposit of bismuth was soon 
obtained. 

Bismuth in nitrate of bismuth. — With bismuth in dilute 
nitric acid, and in a solution of acid nitrate of bismuth, a 
thin deposit of that metal was found in twelve hours. 

Silver in sulphate of copper, and in cyanide of silver 
plating liquid. — With silver in either dilute sulphuric or 
dilute nitric acid on one side, and in a solution of sulphate 
of copper on the other, no deposit of copper took place in 
twelve hours ■ but with silver in a solution of cyanide of po- 



86 The Art of Electro-Metallurgy. 

tassium on one side, and in the double cyanide of potassium 
and silver on the other, a free deposit of silver occurred upon 
the end or piece in the latter solution. 

Antimony in sulphate of copper. — With antimony in 
dilute hydrochloric acid on one side, and in a solution of 
sulphate of copper on the other, a deposit of copper was 
obtained. 

Platinum in nitrate of copper. — With platinum in aqua 
regia on one side, and in either a solution of nitrate of cop- 
per, the ordinary cyanide gilding solution, or a solution of 
tetrachloride of platinum on the other, no deposit of copper, 
gold, or platinum occurred. 

Brass or copper in sulphate of copper. — With brass or 
copper in dilute sulphuric acid on one side, and in a solution 
of sulphate of copper on the other, a deposit of copper was 
obtained in twelve hours ; similarly with copper in dilute 
hydrochloric acid, and in a solution of chloride of copper, a 
metallic deposit occurred. 

Tin in chloride of tin. — With tin in dilute hydrochloric 
acid on one side, and in a solution of stannous chloride on 
the other, a deposit of tin was obtained. 

Copper in sulphate of zinc. — With copper in dilute sul- 
phuric, or dilute nitric acid, on one side, and in a solution 
of sulphate of zinc on the other, no deposit of zinc oc- 
curred in twelve hours. 

Iron in sulphate of zinc, and in sulphate of iron. — With 
iron in dilute sulphuric acid on one side, and in a solution of 
sulphate of zinc on the other, no deposit of zinc was obtained 
in twelve hours ; similarly with iron, dilute sulphuric acid, 
and a solution of protosulphate of iron, no deposit occurred 
in twelve hours. 

Zinc in chloride of zinc. — A piece of zinc was bent so as 
to dip into dilute hydrochloric acid on one side, and into a 
neutral solution of chloride of zinc on the other ; a free de- 
posit of zinc was found upon the end in the metallic solution, 
after a period of twelve hours. 



Methods of Electro-Deposition. %j 

Zinc in sulphate of zinc. — With zinc in dilute sulphuric 
acid, and in a solution of sulphate of zinc, a free deposit of 
the metal occurred in twelve hours. 

Zinc in acetate of zinc. — With zinc in a solution of ace- 
tate of zinc on one side, and in dilute sulphuric acid on the 
other, that in the dilute acid dissolved, whilst the other end 
received a metallic deposit. 

Observations on class of instances No. 3. — 1st, it appears 
that in this class also, we obtain negative as well as positive 
instances ; 2nd, that by this arrangement, unlike the previous 
classes, almost any metal may cause the same metal to be 
deposited — for instance, zinc may deposit zinc, copper de- 
posit copper, and silver deposit silver ; 3rd, that by it even 
a noble metal may cause the deposition of a base metal, 
provided we have a suitable combination of liquids — for 
instance, if a piece of gold or silver be immersed in a strong 
solution of cyanide of potassium on one side, and in a solu- 
tion of sulphate of copper or chloride of antimony on the 
other, the end in the free cyanide solution dissolves, whilst 
that in the copper or antimony one receives a deposit; 
4th, that the metal or end which receives a deposit, derives 
that power from its contact with the metal in the other liquid; 
5th, that, as a general rule, base metals have a greater power 
of causing deposition by this method than the noble ones ; 
6th, that the noble metals are more readily and more often 
deposited than the base ones ; and, 7th, that we may produce 
thick and coherent deposits. 

Method No. 4. — Deposition by two metals and two liquids, 
or 'single-cell process' (see Fig. 20, also Fig. 1, p. 18). 
The following instances belong to the class of deposition 
produced by the immersion of two metals in two liquids, the 
metals being in mutual contact, or connected together by a 
wire, and the liquids separated by a porous partition. 

Zinc depositing antimony. — A piece of antimony was im- 
mersed in a solution of its chloride, and a piece of zinc in 
dilute sulphuric acid, and the two metals being connected 



88 The A rt of Electro- Metallurgy. 

together by a wire, a free deposit of antimony took place in 
twelve hours. 

Iron depositing antimony. — With iron in dilute hydro- 
chloric acid, and antimony in a solution of its chloride, a 
copious deposit of antimony was formed in twelve hours. 

Copper and chloride of antimony or chloride of tin. — 
With copper in dilute hydrochloric acid, and antimony in 
its chloride, or tin in chloride of tin, no deposit of antimony 
or tin occurred in twenty hours. 

Bismuth and chloride of antimony. — With bismuth in 
dilute hydrochloric acid, and antimony in chloride of anti- 
mony, no deposit of the latter occurred in twenty-four 
hours. 

Zinc depositing copper. — With zinc in dilute sulphuric 
acid, and brass in a solution of cupric sulphate, copper was 
deposited. 

Iron and chloride of tin. — With iron in dilute hydro- 
chloric acid, and tin in a solution of its chloride, no deposit 
of tin took place in eighteen hours. 

Tin depositing zinc. — With tin in hydrochloric acid, and 
zinc in a neutral solution of its sulphate, a deposit of zinc 
was obtained in the metallic solution. 

Observations on class of instances No. 4. — 1st, it ap- 
pears that negative as well as positive instances occur in 
this arrangement in common with the others ; 2nd, that 
by using suitable metals and liquids, deposition may be 
effected more rapidly by this method than by the preceding 
ones ; 3rd, that the metal which receives the deposit derives 
its power from its contact with the other metal ; 4th, 
that base metals in strong acids have the greatest power of 
causing a deposit upon the other metals, and noble metals 
the least ; 5th, that the noble metals are more readily de- 
posited than the base ones ; and, 6th, that thick and co- 
herent deposits may be obtained. 

In all the above instances, instead of using one vessel 
divided into two parts by a porous diaphragm, it will be 



Methods of Electro-Depositio7i. 



8 9 



j found convenient to put one of the liquids in an unglazed 
I earthenware porous cell, and immerse the cell in the other 
j liquid (see Fig. 1, p. 18). In this case either liquid may be 
in the outer vessel. 

Fig. 2r. 




MdJwd No. 5. — Deposition by a separate current, or 
* battery process ' (see Fig. 21; also Fig. 2, p. 24). The next 
class o( instances are those in which any of the foregoing 
arrangements, except the first, may be connected by wires 
with two pieces of similar metal immersed in a separate 
liquid. In this class of instances, the method or arrange- 
ment differs from the three preceding ones, simply by 
the wire which connects the two pieces of metal being cut 
in two, and its free ends either immersed in a separate 
liquid, or connected with two pieces of metal dipping into 
that liquid. It is not necessary to have the depositing 
vessel separate ; it may even be attached to the same piece 
of apparatus, provided the liquid in it is perfectly separated 
from the other liquids and metals. The pieces of metal in 
the separate liquid, possess no power of deposition of them- 
selves in that liquid (unless they coat themselves by simple 
immersion), even if they are connected together, but wholly 
derive their power of dissolving and receiving a deposit, 
from the other metals and liquids by means of the current 
passing through the wires. 



90 The A rt of Electro-Metallurgy. 




impound depositing vessels. — In each of the foregoing 
.rangements the deposition is limited to a single vessel, but 
any number of depositing vessels may be connected together 
in a series (see Fig. 22, also Fig. 3, p. 24) so that solution of 
kig. 22. the anode, and deposi- 

tion upon the cathode, 
may be simultaneously 
obtained in every one 
of them by means of 
the same current. It 
was at one time ima- 
gined that this was a 
very economical pro- 
cess, because by this means, with the aid of one equivalent 
of electricity, and at the expense of but one equivalent, each 
of acid and zinc, several equivalents of metal were dissolved 
and deposited; but it was soon found that the process was ren- 
dered so slow, as to neutralise the other advantages, and this 
arrangement therefore is but rarely employed. This practical 
result would have been anticipated by anyone who could have 
interpreted the chemical equivalent of electrical energy. It 
has been recently patented by E. Casselburg (see p. 381). 

General remarks. — In each of the foregoing arrangements, 
the size or shape of the containing vessels, the volume or 
depth of the liquids, or the size or positions of the metals, 
have no material impression upon the production or non- 
production of a deposit ; the temperature, however, is an 
important condition, and in all the experiments I have de- 
scribed, this was about 6o° Fahr. 

Practical points to be observed. — In practical working, ac- 
cording to any one of these methods, it is necessary to attend 
to a number of points based upon the principles already given 
in the theoretical division. We must see that the depositing 
liquid is really an electrolyte, that it has a proper chemical 
composition, and contains the requisite amount of water, free 
acid, free alkali, or is neutral, as the case may be ; that it has 



Practical Points. 



91 



also the proper degree of fluidity, and is at the right tempera- 
ture ; that the strength of the electro- motor is suitable ; that 
the electrodes are of the proper sizes and forms ; that all the 
substances through which the current has to pass will con- 
duct electricity ; that all the points of contact of the wires 
and screws, and the surfaces of the immersed metals, are well 
cleaned ; that the circuit is really complete ; that the elec- 
trodes are in proper positions ; that the current is passing 
in the right direction ; that the different parts of the liquid 
are maintained of uniform composition by stirring, &c. 

There are many metallic solutions, such, for instance, as 
the anhydrous terchloride of arsenic, pentachloride of anti- 
mony, the tetrachloride of tin, &c, which do not conduct 
electricity, and cannot therefore be used as electrolytes. 
Some others are unsuitable from other causes ; for instance, 
those containing nitric acid or a nitrate, are not usually 
good, and sometimes will not yield a metallic deposit at all, 
because of the highly-oxidising character of the liberated 
acid ; chlorates, bromates, and iodates, are also rarely used. 
Iodides are liable to liberate free iodine. Selenates and 
phosphates, also, do not usually form good solutions ; the 
former are apt to have their selenium set free by the de- 
posited hydrogen. Sulphides cannot often be employed, 
because most of them are insoluble ; and those which are 
soluble have a very offensive odour, and are decomposed by 
the atmosphere. Aqueous solutions of chlorides, sulphates, 
and cyanides, are the most usually suitable liquids ; fluorides 
and bromides, are also often available. 

Methods of forming a depositing solution. — There are 
two ways of forming a depositing solution, one termed the 
battery process, and the other the chemical one. In making 
a solution by the former method, the particular metal which 
the liquid is to contain and deposit, is employed as an anode, 
and a current from any suitable source passed through the 
liquid by means of it, until a smooth and clean cathode ot 
suitable metal, receives a sufficient and proper metallic do- 



92 The Art of Electro-Metallui'gy. 

posit. Some operators, in making a solution by the battery 
process, fill a porous cell with the liquid, put the cathode in 
it, and place the porous cell in the larger bulk of liquid ; but 
this is an unnecessary precaution. The chemical method 
consists in preparing the ingredients by chemical means, and 
uniting them in the proper proportions, to form the desired 
solution ; in the use of this method it should always be re- 
membered that freshly-prepared precipitates in a wet state, 
usually dissolve much more quickly, th»n those which have 
been long prepared, or have become dry. 

Method of using a depositing solutio?i (see also p. 341). — If 
a solution contains a very large excess of uncombined acid, or 1 
other solvent, metallic deposition will sometimes not occur, es- , 
pecially if the metal to be deposited is a highly positive one : 
for instance, in a solution of sulphate of zinc, the presence of i 
a large amount of free sulphuric acid will prevent the deposi- i, 
tion of zinc. If on the other hand, a depositing solution con- 
tains no free combining substance, deposition will either pro- 
ceed very slowly, or be entirely stopped, in consequence of an 
insoluble salt (often a non-conducting one) being formed upon 
the anode ; for instance, when an electric current is sent 
through two silver plates immersed in a solution of the pure 
double cyanide of silver and potassium, the dissolving plate 
becomes covered with a white insoluble layer of cyanide of 
silver, which first impedes, and then stops the current. 

If a depositing solution is diluted with water to a very 
large extent, deposition will be greatly retarded, but if, on the 
other hand, it contains a great insufficiency of water, crystals 
of metallic salt will collect upon the anode, especially at its 
lower part, and gradually stop the current. This happens 
in a saturated aqueous solution of cupric sulphate, containing 
copper electrodes and plenty of free acid. 

It is often a great advantage to raise the temperature of 
a depositing solution, because the strength of affinity of the 
liberated negative elements for the anode, increases by eleva- 
tion of temperature, whilst that of the different elements of 



Practical Points. 93 

the electrolyte for each other diminishes. Rise of tempera- 
ture also increases the electric conductivity of an electrolyte, 
and decreases that of the metal plates immersed in it, but, as 
the latter are by far the best conductors, the final effect of 
heating a depositing liquid, is a considerable increase of the 
amount of current passing. 

I have repeatedly observed, that with some solutions 
used hot for depositing, if the cathode was immersed in the 
liquid at 6o° Fahr, and the liquid then heated, no conduction 
or deposition occurred ; nor did it take place if the cathode 
was removed, washed in cold water, and re-immersed. But 
if the liquid was first heated, and then the cathode immersed, 
deposition occurred freely, and the liquid might be cooled 
down considerably without stopping the action. In coating 
iron with tin in some liquids, if the iron was immersed before 
heating the solution, no deposition occurred even at 150 Fahr, 
but if the liquid was first heated, even only to 90 or ioo° 
Fahr., deposition took place. I have not examined whether 
this was due to what has been termed ' the passive state.' 

Usually it is not necessary to screen electro-depositing 
solutions from the direct action of light. In some cases, 
however, light decomposes a liquid, and renders it unfit for 
deposition. ; this is the case with a liquid formed by dissolving 
hyposulphite of silver in a solution of hyposulphite of 
sodium ; cyanide of silver-plating liquids are also affected, 
and turn brown, by the influence of light, but not in such a 
way as to render them unfit for depositing ; the light only 
affects the ' free cyanide ' in them. 

The rapidity of deposition is affected by the superficial 
area of the electrodes, the length and transverse sectional 
area of the intervening solution, and of the connecting wire. 
The larger the immersed surface of the electrodes, the shorter 
the length, and the greater the transverse section of the solu- 
tion, and of the connecting wire, the more rapid is the process. 

The various other conditions, especially that of proper 
density of current, &c, necessary to be secured in order to 



94 The Art of Electro- Metallurgy. 

obtain a metallic deposit, and the desired quality of metal,- 
have been already described in the theoretical section (see 
also p. 341). 



DEPOSITION OF INDIVIDUAL METALS. 
CLASS I. GASEOUS METALS. 

HYDROGEN. 

As there are many persons, students, electro-platers, in- 
ventors and others, who wish to make experiments for them- 
selves, and'require to know what has already been done in 
the separation of particular metals by means of electrolysis, 
the following abstract is given of that portion of the subject. 
1. Hydrogen. — Electro-chemical equivalent weight =1. 
As the separation of hydrogen is a very common result in 
electro-metallurgical operations, and this element is con- 
sidered by most chemists to be a metal, although a gaseous I 
one, and has been called ' hydrogenium ' in order to indicate 
its metallic nature, I include it amongst the metals. Water, 
and all acids may be regarded as salts of hydrogen, and this 
element is set free by electrolysis in many solutions which 
contain water or an acid, in some cases by direct action, and 
in others as a secondary product, being in the latter case 
produced by the action of more electro-positive substances, 
such as the alkali metals, liberated at the cathode, decom- 
posing the water or acid, taking the oxygen, etc. to them- 
selves, and setting the hydrogen free. 

Deposition of hydrogen by simple immersion process. — 
The liberation of hydrogen by contact of the alkali-metals 
with water, is one of the most familiar and striking pheno- 
mena of modern chemistry. The metals of the alkaline 
earths also, usually evolve hydrogen slowly from water, and 
nearly all the base metals also behave similarly, if the water is 
acidulated. Even finely-divided silver, gold, and platinum, 



Deposition of Hydrogen. 95 

set it free from a hot concentrated solution of potassic 
cyanide (H. St. C. Deville). 

Magnesium liberates hydrogen from water; and its amal- 
gam with mercury does so with violence (C. N. Hartley, 
' Chemical News,' vol. xiv., p. 73). Magnesium sets free 
hydrogen from water, especially if the water contains com- 
mon salt, salammoniac, or some acid (Roussin, ' Chemical 
News,' vol. xiv., p. 27). Hydrogen is always evolved, when 
a metal is precipitated from an aqueous liquid by means of 
magnesium (Commaille, 'Chemical News,' vol. xiv., p. 196). 
Finely divided iron (but not either cobalt or nickel), de- 
composes water, slowly at 16 C. but rapidly at ioo° C. 
and liberates hydrogen (Troost and Hautefeuille, ' Chemical 
News,' vol. xxxi., p. 196). 

I have observed, that magnesium does not evolve hydrogen 
in dilute hydrofluoric acid, and but little in an aqueous solu- 
tion of chloride of potassium : but that it evolves it freely, in 
a mixture of the two liquids. Similarly with the same acid, 
and a solution of potassic chlorate. It did not evolve the 
gas, in a mixture of the same acid and perchlorate of potas- 
sium. It liberated hydrogen from a mixture of the acid 
and a solution of bromide of potassium, but not from either 
alone. Similarly with the same acid and iodide of potassium ; 
but not in a mixture of the acid and a solution of potassic 
iodate. In a mixture of hydrofluoric acid and a solution 
of potassic sulphate, magnesium set free hydrogen, but not 
in either liquid singly. According to Deville, even silver de- 
posits hydrogen violently, and forms argentic iodide in liquid 
hydriodic acid ('The Chemist,' New Series, vol. iv., p. 329). 

Deposition of hydrogen by separate current process. — 
Concentrated hydrochloric acid yields chlorine at the anode, 
and hydrogen at the cathode, as direct results of the action 
of the current ; but, according to Bourgoin, the oxygen and 
hydrogen obtained, on passing an electric current by means 
of platinum plates, through distilled water acidulated with 
pure sulphuric acid, are probably not results of an action 
of the curren* upon the water, nor even results of the action 



g6 The A rt of Electro-Metallurgy. 

of liberated electrolytic products upon the water, but of direct 
decomposition of a hydrate of sulphuric acid (see 'Tele-: 
graphic Journal,' vol. i., p. 91, March 15, 1875). 

I have electrolysed on many occasions, pure dilute hydro- 
fluoric acid with electrodes of numerous metals ; and also 
the extremely dangerous liquid, anhydrous hydrofluoric acid, 
with electrodes of palladium, platinum, gold, gas-carbon, &c. ; 
hydrogen was always deposited at the cathode ; the numer- \ 
ous other effects obtained with that acid, will be found de 
scribed under the heads of the respective metals. 

According to Brester, when nitric acid does not liberate ! 
any hydrogen gas at the surface of a cathode of platinum 
or charcoal, by the passage of an electric current, the acid 
is reduced to the state of ammonia (* Chemical News,' vol. 
xviii., p. 144). Bloxam also, has shewn, that the hydro- 
gen evolved from a platinum cathode immersed in dilute 
nitric acid, or in a solution of nitrate of potassium, contained 
in a porous cell, immersed in dilute sulphuric acid containing 
the anode, converts a portion only (not more than one-half), \ 
of the nitric acid of either of those liquids, into ammonia 
(' Chemical News,' vol. xix., p. 289). 

The electrolysis of concentrated formic acid by plati- 
num electrodes, yields carbonic acid and oxygen at the j 
anode, but that of dilute acetic acid gives pure oxygen ; 
aqueous benzoic acid yields oxygen at the anode and hy- 
drogen at the cathode, and the latter sometimes acquires 
a black deposit, which disappears on exposure to light; it is 
probably a hydride of platinum. A saturated aqueous solu- 
tion of oxalic acid, yields twice the bulk of gas at the cathode, 
to that at the anode ; the latter is a mixture of two volumes 
of carbonic anhydride, and one of oxygen. A saturated 
solution of tartaric acid, gives oxygen at the anode, and hy- 
drogen gas with hydride of platinum at the cathode (Brester, 
' Chemical News,' vol. xviii., p. 145). 

Absorption of hydrogen by electro-deposited metals. — As 
hydrogen is often deposited from a solution by electrolysis, 
simultaneously with other metals, electro- deposits frequently 



Deposition of Hydrogen. 97 

contain it. Various experimentalists have observed that 
deposits of palladium and nickel absorb it ; pure tin also in 
a less degree has the same property ; but cadmium, zinc, 
aluminium, copper, lead, silver, mercury, bismuth, gold, and 
platinum (?) do not. The correctness of these statements, 
however, depends largely upon the kind of liquid electrolysed. 
If a piece of palladium, nickel, cobalt, or tin, has a wire of 
aluminium twisted round it, and is then immersed for a few 
minutes in dilute acid, it absorbs sufficient hydrogen to exert 
a slightly reducing action upon a solution of ferri-cyanide of 
potassium. According to Bottger, a palladium plate coated 
with palladium black, absorbs the hydrogen more quickly, 
and when taken from the electrolyte, and dried quickly by 
blotting-paper, becomes red hot in the air in a few seconds. 
I have repeatedly observed that the steel blade of a knife, 
or a steel wire, becomes much more brittle after having been 
made the cathode and evolved hydrogen in an electrolyte, 
and that this occurs not only with a dilute acid but also with 
an alkaline liquid. It is not improbable that steam boilers are 
sometimes weakened by a similar absorption of hydrogen, 
when the water employed in them is decomposed by the 
iron. The explosive variety of antimony formed by electro- 
lysis is also said to contain hydrogen. 



CLASS II. BRITTLE NEGATIVE METALS. 

ARSENIC, TELLURIUM, ANTIMONY, BISMUTH. 

2. Arsenic. — Elec.-chem. eq. = lA = 25. The com- 

3 
monest salts of arsenic are arsenious acid, i.e. the common 
white oxide known as ' arsenic ; ; arsenic acid ; and the 
compounds of those two acids with potash and soda. 
Metallic arsenic itself is a brittle substance, and an inferior 
conductor of electricity. Arsenious acid is soluble in warm 
hydrochloric acid ; also by heating it to dryness with strong 

H 



98 The Art of Electro-Metallurgy. 

nitric acid it is converted into arsenic acid, which is a de- 
liquescent substance, readily soluble in water. 

Deposition of arsenic by simple immersion process. — 
This element is easily deposited by the simple immersion 
process, by dissolving arsenious acid in warm and somewhat 
dilute hydrochloric acid, and stirring the solution with a strip 
of bright copper. This experiment is well known in toxico- 
logical chemistry as being an extremely delicate test for 
arsenic, devised by Reinsch. According to Roussin, from 
solutions of arsenic, magnesium deposits arseniuretted hy- 
drogen, but no arsenic in the metallic state ('Chemical 
News,' vol. xiv., p. 27). 

Deposition of arsenic by the simple contact of another 
metal. — All the arsenic may very easily be extracted from 
arseniferous substances by placing a solution of them in a 
platinum vessel, and immersing in it a piece of zinc in con- 
tact with the vessel ; the arsenic appears on the platinum. 
By prolonging the action the whole of the arsenic is extracted 
('Cosmos,' Second Series, vol. i., p. 595; and ' Chemical 
News,' vol. xii., p. 3). 

Depositmi of arsenic by sepa?-ate current process. — I have 
made many experiments of electrolysis of solutions of arsenic, 
and have obtained from the aqueous fluoride small portions ! 
of a scaly deposit, which appeared to exhibit in a feeble 
degree the peculiar explosive property of the amorphous j 
variety of electro-deposited antimony. 

3. Tellurium— Elec-chem.eq. = — 9 =43'o. Very little 

has been done in the electro-deposition of this metal, pro- 
bably in consequence of the great cost of the substance. 
Ritter could only obtain a pulverulent deposit of it from its 
solutions ; and both he and Sir H. Davy found that, in elec- 
trolysing water by means of an anode of this metal, the water 
surrounding the anode acquired a purple colour, and pre- 
cipitated a brown powder ; Magnus shewed that this powder 
was metallic tellurium. I have electrolysed a pure solution 



Deposition of Antimony. 99 

of its chloride by means of large and smooth platinum elec- 
trodes and a very feeble current, but obtained only a jet- 
black deposit, the inner portion only of which was adherent ; 
the anode was not corroded. I have also electrolysed pure 
dilute hydrofluoric acid with an anode of pure tellurium, by 
a current from a single Smee's cell, and have obtained by 
very slow action most excellent deposits of bright reguline 
metal, of grey colour, and brittle crystalline structure. 

4. Antimony. — Elec-chem. eq. — — =40-66. Its most 

3 
common salts are the oxide, sulphide, terchloride, and po- 
tassic- tartrate (tartar- erne tic). The acid terchloride is the 
ordinary chloride of antimony as prepared for pharmaceuti- 
cal purposes; it is formed thus. — Take one pound of black sul- 
phide of antimony, add to it four pints of hydrochloric acid, 
gently heat the mixture, until the gas decreases, then boil it 
slowly down to two pints, keeping it partly covered all the 
time; cool it, filter it through calico, and keep it in a stoppered 
bottle. It is now a yellowish red liquid (the colour being 
due to iron in the sulphide), of specific gravity about 1*35 to 
1-50. 

A similar solution may be made by the battery method ; 
this consists in passing an electric current from several cells 
through pure and strong hydrochloric acid, by means of a 
large anode of antimony, until a good deposit is obtained 
upon a cathode of platinum of equal surface ; this solution is 
nearly colourless, nearly free from iron, and much more pure 
than the other. A very good solution may also be easily 
made by saturating ten ounces, by measure, of strong hydro- 
chloric acid with freshly-precipitated teroxide of antimony. 
(N.B. Not that made by oxidising antimony by nitric acid, 
nor that which has been long exposed to the air.) Then 
add about five ounces more of the acid to the clear por- 
tion and stir the mixture. About three ounces of the oxide 
will be required. An excellent solution may also be made 
by dissolving an avoirdupois ounce of oxychloride of anti- 



i oo The A rt of Electro-Metallurgy. 

mony in five ounces of pure hydrochloric acid of specific 
gravity fi2. 

The acid chloride of antimony is an excellent conductor 
of electricity ; it dissolves the anode freely, yields plenty of 
bright reguline metal if the battery power is not too strong, 
and its depositing power does not deteriorate by exposure to 
light or air. It is decomposed more or less readily by zinc, 
tin, lead, iron, brass, copper, and german-silver, each of which 
coat themselves with antimony in it by simple immersion, 
Articles immersed in it require to be washed with hydro- 
chloric acid before washing them with water, otherwise the 
latter decomposes the adhering film of liquid, and covers 
the articles with a white insoluble powder. 

The mixed chlorides of antimony and ammonia form a 
very good depositing liquid. It may be made either by 
the battery process, or by mixing two measures of a saturated 
solution of sal-ammoniac with two measures of hydrochloric 
acid and one measure of water, and dissolving antimony in 
it by means of a large anode of that metal and a strong 
battery current, or by simply mixing together equal measures 
of a saturated solution of sal-ammoniac and commercial 
chloride of antimony. This solution conducts well, yields 
plenty of metal of good quality, and does not act so strongly 
upon base metals as chloride of antimony alone, but in other 
respects it is like the chloride. 

The potassic tartrate of antimony (tartar-emetic) is most 
conveniently obtained by purchase. It is a salt not very 
soluble, it requires about fifteen times its weight of water to 
dissolve it ; its aqueous solution is a very bad conductor of 
electricity, and is not to be compared with the chloride for 
depositing purposes ; even with a very feeble electric current 
the deposited antimony consists only of a small quantity of 
a perfectly black powder. On the other hand, however, this 
salt is very freely soluble in a mixture of two volumes of hy- 
drochloric acid and one of water. The solution may be 
made by mixing together about two pounds of water, four 



Deposition of Antimony. 101 

pounds of hydrochloric acid, and eight pounds of the potassic 
tartrate ; or a larger proportion of water may be added if 
desired. This mixture forms an excellent one for depositing 
antimony ; it is a good conductor of electricity, it is not in- 
jured by long-continued working, or exposure to light or the 
atmosphere (I have deposited antimony from it constantly 
during many months) ; it will bear a very strong current 
without the deposit being caused to pass into the state of a 
black powder ; it yields reguline metal rapidly, and in coat- 
ings of any desired thickness (I have obtained deposits from 
it a quarter of an inch thick). Deposits of about one-twelfth 
of an inch in thickness may be obtained in about three days 
and three nights ; articles which are wet with this solution 
may be washed clean in water alone, without requiring to be 
previously washed with hydrochloric acid. 

Deposition of antimony by simple immersion process (see also 
p. 77). — Antimony may easily be deposited from an acid solu- 
tion of its terchloride by the simple immersion process. In 
this way a solution of chloride of antimony is used for impart- 
ing a lilac colour to articles of brass. A large quantity of water 
is added to a small quantity of chloride of antimony, which 
causes a dense white precipitate of oxychloride of antimony ; 
the mixture is boiled until the whole is nearly redissolved, 
more water is added to the solution, and again boiled m like 
manner. After being filtered, this clear liquid is raised to the 
boiling point, and the articles of brass, previously cleaned, are 
immersed in it; they immediately deposit a film of antimony 
of a lilac colour upon themselves by the simple immersion 
process, and are allowed to remain a greater or less length 
of time according to the tint required. They are then well 
washed in clean water, dried in hot sawdust in the usual 
manner, and protected from alteration of colour by lacquering. 
Terchloride of antimony is also used for bronzing gun-barrels. 

Antimony powder, deposited by simple immersion process 
from its chloride by means of zinc, is used for imparting an 
appearance of grey cast-iron to figures of plaster-of-Paris. 



I o 2 The Art of Electro- Metallurgy. 

According to Roussin, magnesium deposits antimoniuretted 
hydrogen, but no metallic antimony, from solutions of anti- 
mony (' Chemical News,' vol. xiv., p. 27). I have observed 
that crystals of silicon did not become coated with antimony 
in a solution of fluoride of antimony containing free hydro- 
fluoric acid ; that zinc deposited antimony as a black powder 
by simple immersion in a solution of the mixed fluorides of 
antimony and potassium ; and that the oxide of iron was 
rapidly dissolved from a rusty iron wire in a mixture of equal 
measures of solution of terchloride of antimony and a satu- 
rated solution of sal-ammoniac. 

Watt coats copper with antimony by simple immersion 
thus : Dissolve one ounce of chloride of antimony in one 
pint of spirit of wine, and add hydrochloric acid until the 
liquid is clear. Immerse the clean article in it during about 
half an hour ; it receives a bright coating. 

Gold in contact with antimony, in a solution of cold or 
boiling salt of antimony, does not acquire a coating of metal 
(Raoult, ' Chemical Society's Journal,' vol. xi., p. 465). 

Deposition of 'antimony by separate curre?it process (see also 
pp. 81, 87, 89). — In depositing antimony by the battery pro- 
cess, the metal may be obtained not only in a state of loose 
black powder, but also in two distinctly different, coherent, 
reguline conditions, viz., as a very brittle metal of a 
grey-slate colour, and hard crystalline structure ; and also 
as a highly lustrous steel-black deposit, of amorphous struc- 
ture, and somewhat less hard than the pure variety ; which 
retains its colour and brightness without oxidizing for a long 
time. 

A satisfactory solution for obtaining the pure grey metal 
is composed of : — 

Distilled water 12 ounces. 

Tartar-emetic I ounce. 

Tartaric acid . . r . . I ,, 

Pure hydrochloric acid . . . ii ,, 

It is not a good conductor, and should be worked slowly 



Explosive Antimony. 1 03 

with two Smee's elements, at such a rate as to deposit about 
one-eighth of an inch thick of the metal in four weeks. 

Whilst engaged in depositing antimony from an acid solu- 
tion of the terchloride by the separate current process, in 
October 1854, I observed a singular development of heat 
by the deposited metal when scratched or rubbed, and pub- 
lished a brief account of it in the i Philosophical Magazine' for 
January 1855. I afterwards investigated the phenomenon 
more fully ; and the following account, condensed from the 
' Transactions of the Royal Society ' contains all the leading 
facts relating to it. 

The best solution for forming the strongly-thermic 
variety of deposit is composed of one avoirdupois ounce of 
teroxide of antimony or oxychloride of antimony, dissolved 
in five or six ounces of hydrochloric acid of sp. gr. 1*12 ; or 
it may be made by saturating two measures of hydrochloric 
acid with oxide or oxychloride of antimony, and then add- 
ing one measure more of the acid. 

If, instead of the terchloride solution, a solution of either 
terbromide or teriodide of antimony is employed, the de- 
posited coating possesses a similar property of evolving heat, 
but in a much less conspicuous degree, especially the deposit 
from the teriodide; and if a solution of fluoride of antimony 
is employed, the deposited metal is of a grey colour, perfectly 
crystalline, and entirely destitute of the peculiar heating 
property. Under some circumstances this crystalline variety 
of deposit may also be obtained by electrolysis from a weak 
solution of terchloride of antimony, especially if the battery 
power is very feeble, or the liquid is employed in a dilute or 
heated state. 

In common with electro-deposits generally, the inner 
and outer surfaces of both the black and grey deposits are in 
unequal states of cohesive tension, frequently in so great a 
degree as to rend the deposit extensively, and raise it from 
the cathode in the form of a curved sheet, with its concave 
side towards the anode. This state of tension is most mani- 



1 04 The A rt of Electro- Metallurgy. 

fest with rapidly-formed, thin deposits, especially upon 
extended flat surfaces. 

It is worthy of notice that if the speed of deposition was 
gradually diminished to about 0-5 grain per square inch of 
cathode per hour, when it attained a certain degree of slow- 
ness (about 07 grain per square inch per hour), the charac- 
ter of the metal depositing suddenly changed from the 
amorphous black to the crystalline grey variety without ex- 
hibiting the slightest gradation between, and the two layers 
of active and inactive metal might be readily separated by 
means of a knife. With deposits very rapidly formed, the 
fractured surface was coarse and less black, and the thermic 
change was found to be very strong, shattering the metal 
with almost explosive violence. 

Faint crackling sounds frequently issued from the depo- 
siting metal, evidently caused in most instances by the co- 
hesive action just mentioned, and in other cases they were 
due to the sudden expulsion of bubbles of gas from holes in 
the deposited metal, especially with the bromide variety, or 
by depositing upon an iron cathode in the terchloride solu- 
tion. The deposit obtained in the bromide solution was 
frequently perforated with holes all over its surface, and had 
the appearance of a metallic sponge caused by the numerous 
bubbles of gas. The thermic property of the deposit from 
the terchloride gradually disappears, the substance in a 
state of powder loses its power in six months ; fragments one- 
sixteenth of an inch thick lose their power in the course of 
twelve months, whilst others a quarter of an inch thick still 
possess a portion of their heating power at the end of three 
or four years. 

Each of the varieties of active antimony is fragile and 
easily broken; that from the iodide solution is extremely so. 
Thin pieces, one-sixteenth of an inch, of the chloride variety 
may be broken in the air at 6o° Fahr. without discharging 
their heat, if broken with care; thicker pieces should be 
broken under the surface of cold water, by gentle blows with 



Explosive A ntimony. 105 

wood, or other substance not very hard. Very thin pieces may 
with care be reduced to fine powder in a mortar under a 
mixture of ice and water, and the powder so produced, after 
drying in a thin layer in a slightly warm place, possesses all 
the heating properties of the original solid mass. 

Heating the chloride variety to 212 Fahr. for one hour 
in boiling water, or keeping it at a somewhat lower tempera- 
ture (185 or 19 o° Fahr.) for a longer period in an air-bath, 
causes it gradually to evolve its heat, and lose its peculiar 
heating power. 

A cylindrical bar of the chloride variety, about half an 
inch in diameter, formed upon a rod of grain tin one-eighth 
of an inch thick, when changed by the momentary contact 
of a heated wire, evolved sufficient heat to melt the tin com- 
pletely, and the tin ran out through a crack in the antimony, 
and remained liquid a short time. 

By applying momentary heat to the ends of deposits 
formed upon heliacal copper wires, the action was gradually 
transmitted to the opposite ends at a speed varying from 
twelve to thirty feet per minute, the rapidity of progress 
depending chiefly on the absence of cooling influences, 
cracks in the metal, and portions of grey crystalline deposit. 

The specific gravity of the active chloride variety varied 
from 5739 to 5*944 ; but after having been discharged sud- 
denly of its heat, its specific gravity varied from 5748 to 
6*029. The specific gravity of the inactive or pure crystalline 
variety varied from 6*369 to 6*673. 

Their electro-chemical equivalents, determined by elec- 
trolysing their solutions simultaneously in the same circuit 
with a solution of sulphate of copper, and weighing the 
deposits, were 42*30 to 43*81 parts of the active variety, and 
40*41 to 40*79 parts of the crystalline kind for every 31*7 
parts of copper deposited in the copper solution. 

The peculiar change in the active chloride variety is 
attended by alterations in the colour, cohesion, and fractured 
surfaces in the substance ; from a bright steel colour and 



1 06 The A rt of Electro-Metallurgy. 

glassy fracture, it passes to a dull grey colour and granular 
fracture, and its cohesive power greatly increases. These 
changes occur whether the heat has been evolved suddenly 
or very gradually by long lapse of time. Similar effects are 
observed, but in different degrees, with the bromide and 
iodide deposits ; straight bars of the active chloride variety 
suddenly discharged become curved by the heat, the outer 
side, or that last deposited, invariably becoming concave ; 
this is similar to the effect of annealing upon electro- 
deposited metals generally. 

The heat evolved by the peculiar change in the chloride 
variety is not due to cohesive action ; for it has been found 
that the amounts of heat evolved by similar weights of the 
substance in a single solid mass, in small pieces and in fine 
powder, in a calorimeter, were not sensibly different. Nor 
is the heat due to alteration of the specific heat of the sub- 
stance during the change. 

The temperature to which the active chloride variety must 
be raised, either locally or throughout its mass, to produce the 
sudden discharge, varies according to several circumstances, 
but is generally about 2 oo° or 210 Fahr. in an air-bath. 
The discharge is not limited to one particular temperature, 
but commences between 170 and 190 , and gradually 
increases in rapidity by rise of temperature to some point 
about 200 or 210 Fahr., when it attains its maximum, and 
discharges all its remaining heat suddenly. A rod of the 
substance may be gradually discharged of its heat at one 
end, without discharging the opposite end, by immersing 
that end for one hour in nearly boiling water. 

The total amount of heat evolved by the sudden discharge 
of the chloride variety was considerable, and was sufficient 
in most instances to raise the temperature of an equal weight 
of ordinary antimony of specific heat 0*0508, about 650 or 
700 Fahr. degrees, and in one instance 705-89 Fahr. degrees, 
above the atmospheric temperature (6o° Fahr.) at which it 
was discharged. 



Explosive Antimony. 107 

When the active chloride variety is suddenly discharged 
of its heat, there is invariably evolved from it a small quan- 
tity (generally about 3-5 per cent.) of vapour, consisting 
almost entirely of terchloride of antimony. This evolution 
of vapour is not a cause but an effect of the heat. 

The following are the results of two analyses of specimens 
of amorphous antimony, obtained from an acid solution of 
the pure chloride : — 
No. 1. 



Sb . 93-36 

SbCl 3 . .5-98 

HC1 . . 0-46 

99-80 



= 6-44 



No. 2. 

Sb . . . 93-51 
SbCl 3 . .6-03 
HC1 . . o^i\ 

9975 



The second variety of active antimony may be obtained 
as follows : dissolve one part of teroxide of antimony in ten 
parts of hydrobromic acid, of specific gravity about 1*3 ; 
filter the solution, and electrolyse it by means of three 
Smee's elements, and an anode of antimony, at a speed of 
deposition of about 3 to 5 grains per square inch of receiving 
surface per hour. 

This variety is of a lighter colour than that from the 
chloride, and is generally quite dull in aspect. It exhibits 
less of the cohesive cracking action than the first kind, and 
is less hard. Its specific gravity at 6o° Fahr. varies from 5 "4 15 
to 5-472. 

By momentary contact of a red-hot wire, it exhibited a 
similar molecular and thermic change, but the action did not 
spread throughout the mass unless it was previously raised to 
a temperature of about 250 Fahr. ; if then touched with the 
wire it evolved all the heat instantly, with explosive violence 
and projection of pieces of the substance. Scratching the 
heated substance by a steel pointer did not cause it to dis- 
charge its heat. Pieces heated upon mercury, or melted 
fusible alloy, discharged themselves suddenly and powerfully 
when the bath attained a temperature of about 320 Fahr. 



I o 8 The A rt of Electro-Metallu rgy. 

By fusion in a bent tube of refractory glass, it was found 
to consist of 79*52 per cent of metal and 20*48 per cent. of v 
volatile matter— a colourless, buttery substance, slightly semi- 1 
fluid at 6o° Fahr., which doubtless consisted of terbromide 
of antimony and a little aqueous hydrobromic acid. Other 
ispecimens treated thus gave respectively 18*42 and 20*40'; 
per cent, of volatile matter ; the two specimens being part 1 
of a single deposit, the first being from the upper and the ! 
second from the lower part of the deposit, as it was sus- 
pended in the electrolyte. 

The electro-chemical equivalent of this variety was 
determined by depositing it simultaneously by the same 
current with the chloride variety, and ascertaining the 
relative weights of the two deposits. In two experiments of 
this kind there were obtained respectively 50*09 and 50*11 
parts of this variety for every 42 -5 parts of the active chloride 
variety, or 32*2 parts of zinc consumed. And in two other 
determinations 51*2 and 51*4 parts of bromide deposit were 
obtained. Each of these quantities of deposit contained the 
same amount of metallic antimony, viz. 40 parts or one-third 
of an atomic weight ; the remainder being the associated 
salt of antimony . These results indicate that the pure metal 
alone is deposited by the current. 

The third variety of heat giving electro-deposited anti- 
mony was obtained as follows : Dissolve one part by weight 
of teroxide of antimony in fifteen parts of hydnodic acid, of 
specific gravity 1*25, and electrolyse it at a speed not ex- 
ceeding one grain per square inch of cathode per hour. 

The deposit is scaly-grey, dull in appearance, very 
friable, and much less metallic in character than either of 
the other kinds, unless it has been deposited with extreme 
slowness. The specific gravity of a slowly-formed specimen 
was 5*27. On immersing dry pieces in water a hissing 
sound, as of strong absorption, occurred, and numerous bub- 
bles of gas issued from all parts of its surface during a few 
seconds. The tendency to evolution of hydrogen gas in the 



Explosive A ntimony. 1 09 

solution by this variety is so great as frequently to disinte- 
grate the deposit completely. 

Pieces one-ninth of an inch thick required to be heated 
upon mercury to 338 Fahr. before the contact of a red-hot 
wire would cause a discharge of heat ; it then discharged 
but feebly, with evolution of red vapours of iodide of anti- 
mony. 

By fusing the unchanged substance in a glass tube, it 
yielded 7776 per cent, of metal, and a solid, red, easily 
fusible sublimate, together with a little moisture, evidently 
teriodide of antimony, and a little aqueous hydriodic acid. 

Its electro-chemical equivalent was determined in the 
same way as the previous kind. With slow action (0*5 
grain per square inch of cathode per hour) 5 03 9 parts of 
deposit were obtained, and with very slow action (0*2 grain 
per square inch per hour) 48*07 parts were obtained for 
every 42-5 parts of deposit in the chloride solution. 

The explosive kind of antimony electro-deposited from 
the chloride solution has been several times rediscovered in 
America and other places by different persons. 

Amorphous antimony is one of the easiest of metals to 
deposit in a firm, coherent state. Its appearance when 
deposited from the chloride, or from the solution of the 
potassic-tartrate in hydrochloric acid, by means of the cur- 
rent from two or three of Smee's elements and an anode 
of antimony, is very beautiful, and when deposited at a 
proper speed it has much the appearance of highly-polished 
steel. The process should be continued until the coating is 
about one-twelfth of an inch in thickness on each side of a 
thin sheet of bright copper, employed as the cathode: this 
will occupy about three days and nights if the current is 
suitably strong. The solution should be stirred with a 
rod of gutta-percha each morning and evening during the 
action. Sometimes a deposit explodes in the liquid during 
its formation. 

When the deposit is sufficiently thick, transfer the coated 



HO The A rt of Electro-Metallurgy. 

sheet to a wooden or gutta-percha bowl into which a stream of: 
cold water is freely running, and clean the metal by first pouring 
dilute hydrochloric acid over it, and washing it in the cold 
water with the aid of a soft brush. By bending the sheet of 
metal very slowly in the water, the antimony falls off in large 
plates, which may be broken into smaller pieces upon a con- 
cave surface of wood under cold water by a gentle blow with 
the end of a wooden rod. Each fragment after washing and 
drying (without the aid of heat) should be wrapped in cotton 
wool, and kept in a cool place. It gradually, during many 
months, loses, more or less, its heating property and bright- 
ness," and acquires an acid reaction. 

A singular phenomenon sometimes occurs in depositing 
explosive antimony. As the solution is a very dense one, 
if it is rapidly worked, the exhausted liquid rises to the top 
and lies in a layer upon the surface, and, if the solution is 
not occasionally stirred, a film of deposited metal forms 
around the cathode upon the surface of the liquid in the 
form of a button one and a half inch in diameter. 

I have frequently deposited collections of shining grey 
crystals of the pure variety of antimony from a saturated 
neutral solution of the fluoride, by means of a current from 
six Grove's or ten Smee's elements ; also from a dilute solu- 
tion containing free hydrofluoric acid, by a current from two 
Smee's cells. As these crystals have a beautiful appearance 
and do not oxidize, some practical use might probably be 
made of them for the purpose of ornamentation. 

For a full account of the properties of electro-deposited 
antimony see 'Phil. Trans. Roy. Soc.' 1857, 1858, and 1862 ; 
'Chemical News/ vol. viii., pp. 257 and 281 ; also 'Journal 
of the Chemical Society.' 

Both the black and red sulphides of antimony dissolve 
in hydrosulphate of ammonia, and the resulting solutions 
conduct very freely with an antimony anode, and one Smee's 
element, but yield no metal even with a current from twenty- 
five cells in series. Aqueous solutions, either of caustic 



Deposition of Bismuth. 1 1 1 

potash, tartrate or oxalate of potassium, scarcely conduct 
at all with an anode of antimony, and the current from one 
or two Smee's elements. Cyanide of antimony dissolved in 
a solution of cyanide of potassium has been proposed as a 
depositing solution, but I have found a solution of cyanide 
of potassium to be a very bad conductor with an anode of 
antimony. 

A solution composed often litres of water, 500 grammes 
of finely-powdered sulphide of antimony, and 2000 grammes 
of carbonate of sodium, dissolved by boiling, filtered whilst 
hot, and electrolysed at a boiling temperature, has also been 
recommended (Roseleur's ' Galvanoplastic Manipulation,' p. 
282) for depositing antimony. 

Antimony used as an anode in water becomes covered 
with oxide. Fused oxide of antimony yields antimony at 
the cathode, but antimonic acid is formed at the anode, and 
stops the current. According to Faraday, fused terchloride of 
antimony conducts badly and is but little decomposed. I 
have observed that electro-deposited antimony did not spread 
over the blackleaded surface of gutta-percha. 

5. Bismuth. — Elec.-chem. eq. = = 70. The com- 
monest salts of bismuth are the basic nitrate (pearl white 
or mineral cosmetic), the acid nitrate, and the chloride. 
The basic nitrate is formed by treating the acid nitrate with 
abundance of water ; it is a white powder, soluble in nitric 
or hydrochloric acid. The acid nitrate is made by digesting 
the metal in warm dilute nitric acid, evaporating and crystal- 
lising the solution. The chloride may be made by dissolv- 
ing bismuth in a mixture of four measures of hydrochloric 
acid and one of nitric acid, and expelling all excess of acid 
by evaporation. 

Deposition of bismuth by simple immersion (see also p. 77). 
— Magnesium deposits pure metallic bismuth from solutions of 
bismuth salts (Commaille, ' Chemical News/ vol. xiv., p. 188). 
* To coat articles of tin with bismuth by simple immersion : 



112 The A rt of Electro-Metallurgy. 

dissolve ten grains of nitrate of bismuth in a wine-glass full 
of distilled water, to which two drops of nitric acid have been I 
added. Immerse the articles ; the bismuth will at once 
begin to be deposited upon them in very small, shining 
plates.' 

Deposition of bismuth by a separate current (see also pp. 82, 
85, 88). — I have deposited this metal bymeans of an extremely 
feeble current, from a solution of the nitrate in water, with 
nearly the minimum amount of free acid. The metal was then 
reguline, and appeared very beautiful, white, with a faintly 
pinkish tint, and with a fine silky lustre, but the coating was 
rather thin ; the deposit would not spread over a blackleaded 
surface in the liquid. According to some writers, such a 
deposit is liable to explode when struck. I have also de- 
posited it from a solution of iodide of bismuth and iodide 
of potassium, and obtained an extremely bulky, jet-black 
powder, which contained iodine after persistent washing, and 
slowly oxidized and became greyish white in the air after many I 
months. 

Pure dilute hydrofluoric acid, with an anode of bismuth, ; 
and a current from a single Smee's element, conducted very | 
badly indeed, and yielded only a black film upon a copper ! 
cathode in thirty hours. 

A cyanide solution has been recommended for depositing 
this metal, but a bismuth anode does not dissolve readily in 
a hot solution of cyanide of potassium. 

The current from two DanielPs cells passed through a 
solution of basic nitrate of bismuth, and tartrate of sodium, 
gave a deposit of hydrated peroxide of the metal upon an 
anode of platinum (W. Wernicke, ' Journal of Chemical 
Society,' vol. ix., p. 307; ' Chemical News,' vol. xxii., p. 240). 

Fused oxide of bismuth, electrolysed with copper elec- 
trodes, deposits bismuth upon the cathode ; with platinum 
electrodes the cathode forms a very fusible alloy with the 
deposited metal (P. Buckhard, ' Chemical News,' vol. xxi., 
p. 238). 



Deposition of Noble Metals. 1 1 3 

According to M. A. Bertrand, metallic bismuth may be 
deposited upon copper or brass from a solution composed 
of thirty grains (grammes ?) of the double chloride o r bis- 
muth and ammonium, dissolved in a litre of water slightly 
acidified with hydrochloric acid, by means of a current from 
a single Bunsen's cell. He states that antimony may be 
deposited in a similar manner ('Athenaeum/ April 22, 1876, 
p. 570). He recommends its use for artistic decorations, 
instead of platinum-black. 

CLASS III. NOBLE METALS 

OSMIUM, RUTHENIUM, RHODIUM, IRIDIUM, PALLADIUM, 
PLATINUM, GOLD, SILVER, MERCURY. 

6. Osmium. — Elec.-chem. eq. = -~~ = 33*16. Scarcely 

anything has been done in the electro-deposition of this metal. 
F. Wohler employed it as an anode in the electrolysis of 
dilute sulphuric acid, with a current from two Bunsen's cells, 
and found it freely converted into osmic acid (Os 4 ), but 
with a solution of caustic soda as the electrolyte, the liquid 
became of a deep yellow colour, and metallic osmium was de- 
posited upon the cathode (' Chemical News,' vol. xix., p. 10.) 
Smee electrolysed a solution of osmic acid, and obtained a 
b)ack deposit. 

7. Ruthenium. — Elec-chem. eq. = I^L 2 = 26'o5. Ac- 
cording to the same authority, ruthenium behaves like osmium. 

8. RJiodium. — Elec-chem. eq. = "^-^ = 26*07. Smee 

3 
deposited this metal from a solution of its sodio-chloride,and 
obtained a brittle white deposit by a current from ten cells with 
platinum electrodes ; with a stronger current the deposit was 
a black powder. According to a writer in Dingler's 'Poly- 
technic Journal,' electro-deposited rhodium (and iridium) 
detonate when heated (see ' Journal of Chemical Society, 

i 



1 14 The A rt of Electro-Metallurgy. 

vol. xi., p. 1007), probably in consequence of their contain- 
ing hydrogen. 

9. Iridium. — Elec-chem. eq. = 1^7 = 49-25. Smee 

4 
states that he has reduced this metal in a bright reguline state 
on a small scale. According to F. Wohler, osmi-iridium is 
readily dissolved as an anode in a solution of caustic soda 
(' Chemical News,' vol. xix., p. 10). 

10. Palladium. — Elec-chem. eq. 1^—5 = 26*62. A 

4 
suitable depositing solution may be made by precipitating and 
redissolving chloride of palladium by an excess of a solution 
of potassic cyanide, or by sufficiently saturating a solution 
of cyanide of potassium with the metal by the battery 
process. The solution dissolves a considerable quantity of 
the metal, and is said to yield thick metallic deposits in a 
white reguline state. 

The ammonio-chloride is also a good salt for the purpose, 
and should be worked with a palladium anode, and a 
current from two or three cells ; the current is a little im- 
peded in this solution by a bright golden yellow powder 
forming upon the anode. Palladium nitrate is less fitted for 
electro-metallurgy, because it acts more freely upon base 
metals, and is apt to yield the metal as a black powder ; it is 
however a good conductor of the current. Iodide of palla- 
dium dissolved in a solution of iodide of potassium is still 
less satisfactory. M. A. Bertrand recommends a perfectly 
neutral solution of double chloride of palladium and ammo- 
nium, for electro- deposition of palladium, either with or with- 
out the use of a battery (' Chemical News,' vol. xxxiv. p. 227). 

Palladium used as an anode in dilute sulphuric acid, 
with a current from two Bunsen's cells, becomes slowly 
covered with an almost black film of peroxide of palladium 
(Pd O2) (F. Wohler, 'Chemical News/ vol. xix., p. 10). 

T have electrolysed pure dilute aqueous hydrofluoric acid 
containing about 30 per cent, of the anhydrous acid, by 
means of a current from six Smee's elements, and a small sheet 



Electrolysis of Anhydrous Hydrofluoric A cid. 1 1 5 

of palladium as anode, in a large platinum cup as cathode. 
Conduction was free, much gas was evolved from each elec- 
trode, and there was a strong odour of ozone. A dark red- 
brown film quickly formed upon the anode, but did not dis- 
solve after fifteen hours of action ; the liquid was black by 
being filled with floating particles of metallic palladium. 
After six days' action the anode was greatly corroded. In 
the electrolysis of aqueous hydrofluoric acid, by means of a 
palladium anode and platinum cathode, two effects occur : 
First, the water is decomposed, oxygen being evolved at the 
anode and hydrogen at the cathode. Second, hydrofluoric 
anid is decomposed also, the fluorine uniting with the 
anode, and the hydrogen escaping at the cathode ; and the 
stronger the acid, the less is the proportion of the water 
decomposed to that of the acid. 

As this process offered a very likely means of obtaining 
fluorine itself, I electrolysed pure anhydrous hydrofluoric 
acid on several occasions, with a thick sheet of palla- 
dium as the anode, and the platinum-containing vessel as the 
cathode. This process was difficult and very dangerous ; in 
each case it was conducted in the opening of a chimney, 
and the platinum vessel containing the acid was immersed in 
a large bulk of a freezing mixture, composed of ice and 
chloride of calcium. Notwithstanding the low temperature 
employed, and the vessel being closely covered by a lid of 
paraffin, the acid volatilised rapidly, partly in consequence of 
the escaping hydrogen, and the heat evolved by the passage 
of the current. The coldness of the vessel and the intense 
attraction of the acid vapour for moisture caused drops of 
water to condense upon the lid of the vessel, and made it 
difficult to preserve the acid in a perfectly anhydrous state ; 
the lid was therefore made so as to overhang the outer edge 
of the vessel, and had laid upon it a layer of cotton wool to 
absorb the moisture. 

In the three first experiments the platinum cup was 
usually about three and a quarter inches deep and one and 



1 1 6 The A rt of Electro-Metallurgy. 

three-quarters inch wide, and the whole of its bottom part 
inside was occupied by a shallow dish of paraffin. The 
battery consisted of from six to thirty Smee's elements ; 
with twenty and upwards the conduction was copious. In 
each experiment, with a strong current, the anode quickly 
became coated with a dark, red-brown, brittle crust, which 
was of a redder colour on the side next the anode. 
As the coating entirely covered the immersed part of the 
anode, and did not greatly diminish the current, either it or 
the acid in its pores freely conducted electricity. The 
crust was scraped off, at intervals of half an hour or an hour, 
into a platinum dish, standing upon a heated slab of iron, in 
order to dry it quickly, and at once transferred to a perfectly 
closed platinum bottle. The heated dish should not be at a 
temperature much exceeding 300 or 400 Fahr. In each 
instance, some black powder collected upon the cathode and 
in the paraffin dish, and was found to be metallic palladium. 
From the small amount of deposit upon the cathode, 
and the absence of colour in the liquid, after eleven hours' 
action, it was evident the crust was but little if at all soluble 
in the anhydrous hydrofluoric acid ; the crust found in each 
experiment was nearly black when dry, and shewed signs of 
metallic particles when rubbed between smooth surfaces of 
agate ; it is probable that the crust was partly decomposed 
by contact with hydrogen from the cathode. 

The most perfect forms of experiment to exclude the 
reducing effect of the hydrogen were made with a platinum 
cup two and three-quarters inches wide and three and a 
quarter inches deep, divided into two equal parts by a 
well-fitting, thin, vertical plate of paraffin, extending to 
within half an inch of the bottom, and covered by two half 
circles of that substance. The palladium anode and plati- 
num cathode were each about four inches long and one inch 
wide, and firmly fixed in slits in the two halves of the cover. 
With five and a half ounces of the perfectly anhydrous acid, and 
a current from twelve one-pint Grove's elements, the conduc- 



Electrolysis of A nhydrous Hydrofluoric A cid. 1 1 7 

tion was copious, and in five minutes the part of the anode 
in the acid had acquired a deep-brown colour. The electro- 
lysis was continued during five hours, the anode being taken 
out and scraped each half-hour. The crust was hard, and a 
few sparks were produced on some occasions by particles of 
the hot crust being decomposed by the heat of friction in 
removing it. A hissing sound was heard during the whole 
of the electrolysis, but the fume of the acid prevented any 
effervescence being seen. 10-46 grains of black powder 
was found upon the cathode and adjacent parts of the con- 
taining- vessel and partition, and yielded 1011 grains of 
metallic palladium. The anode had lost 37*90 grains in 
weight, and 54*13 grains of the dry brown crust was obtained. 
1*37 grain of the crust, gently heated in a platinum lid 
under a glass cover, generated a red heat in itself, emitted 
sparks, also a vapour which attacked glass powerfully, and 
left a black powder weighing i - i4 grain, which by heating to 
full redness evolved a pungent acid odour, and left about -87 
grain of pinkish metallic palladium. These numbers are in 
the proportion of 61 -2 parts of expelled substance for each 
106*5 parts of residual palladium. 

I also found that a palladium anode was very rapidly 
caused to corrode by the passage of a current from three to 
six Grove's elements through pure fluoride of potassium in a 
state of fusion ; and finely divided palladium was found in 
the saline residue. 

I electrolysed strong nitric acid by means of a current 
from fifty Smee's elements, with a palladium anode and a 
platinum cathode. Copious conduction, and rapid decom- 
position of the acid, with abundant evolution of red fumes, 
took place. Much gas was evolved from the anode, but 
none from the cathode, until after a short time. The anode 
was not at first visibly corroded, but after half-an- hour's 
action the palladium slowly dissolved, forming a red liquid. 
No deposit formed upon the cathode. With either strong 
or partly diluted hydrochloric acid, instead of nitric, there 



1 1 8 The A rt of Electro- Metallurgy. 

was instant and rapid action, copious evolution of hydrogen 
at the platinum cathode, and chlorine at the palladium anode, 
and the latter dissolved, forming a blood-red liquid, and 
there quickly appeared a black deposit of palladium upon the 
cathode. With dilute sulphuric acid the conduction was 
copious, and a deposit of splendid colour, red, purple, &c. 
formed upon the anode, but no odour of ozone was evolved 
unless the anode dipped only a very small distance into the 
liquid. By making the sheet of palladium the cathode for a 
short time, the now well-known phenomenon of bending 
by absorption of hydrogen took place, and on taking it out 
and bending it by mechanical means it suddenly evolved 
much heat. 

ii. Platinum. — Elec-chem. eq. = I9 ^ = 49-25. The 

4 
only common salt of platinum is the tetrachloride, made by 
dissolving scraps of platinum in a hot mixture of one volume 
of nitric acid and two and a half volumes of hydrochloric 
acid, until the liquid acquires a deep-red colour, and then 
evaporating the solution nearly to dryness, and allowing it to 
cool and solidify ; it is a deep-red salt, very freely soluble 
in water. The other salts of platinum are usually made 
from it. 

There are two names applied to the electro-deposition 
of platinum, viz. platinising and platinating; by the former 
is usually meant its deposition as a black powder or film, 
and by the latter its precipitation as white reguline metal. 

For platinising either by simple immersion, or more 
rapidly by the aid of a separate current or battery, we may 
use the tetrachloride dissolved in water, containing one- 
fourth its volume of nitric acid, or dissolved in water alone. 
Smee appears to have been the first to platinise sheets of 
silver for the negative plates of voltaic batteries. 

Deposition of platinum by simple immersion (see p. 77). — ■ 
Nearly all the common metals become coated with platinum 
by simple immersion in solutions of platinum. 



Deposition of Platinum. 119 

A deposit of platinum in the reguline state is more diffi- 
cult to obtain than one of either copper, silver, gold or nickel. 
Bright platinum, but of a dark colour, may be obtained upon 
clean copper articles by immersing them in a boiling solution, 
composed of 100 parts by weight of distilled water, twelve of 
caustic soda, and ten of the tetrachloride of platinum ; forty 
parts of sodic carbonate may be substituted for the twelve 
parts of caustic soda. 

Or add to a strong solution of the platinum chloride, 
carbonate of soda in fine powder, until effervescence ceases ; 
then add some glucose, and afterwards as much chloride of 
sodium as will produce a whitish precipitate. Place the 
articles of copper or brass which are to be coated in a zinc 
colander, and immerse them thus for a few seconds in the 
mixture, which should be at a temperature of 6o° C. (=140° 
Fahr.) Then wash the articles, and dry them in hot saw- 
dust (Les Mondes, ' The Chemical News/ vol. xix. p. 226). 
Magnesium deposits pure platinum from a solution of 
platinic chloride (Commaille, ' Chemical News/ vol. xiv. p. 
188). I have observed that crystals of silicon did not 
deposit platinum from a solution of tetrachloride of pla- 
tinum. 

Deposition of platinum by separate current (see pp. 82, 89). 
— Probably the best solution for obtaining thick reguline de- 
posits is that employed by Roseleur, and obtained as follows. 
Convert ten parts by weight of platinum into dry tetrachloride 
in the manner already described, dissolve it in 500 parts of 
distilled water, and filter if necessary. (N.B. If there is much 
sediment, the salt has been dried either too much or care- 
lessly.) Dissolve also 100 parts of crystalline phosphate of 
ammonia in 500 parts of distilled water, and add it, with 
stirring, to the platinum solution; this produces a copious 
precipitate ; then add at once, with stirring, a previously pre- 
pared solution of 500 parts of phosphate of soda crystals in 
1000 parts of distilled water. Boil the mixture until the 
odour of ammonia ceases, and the liquid which was pre- 



1 20 The Art of Electro-Metallurgy. 

viously alkaline begins to redden blue litmus paper; the 
yellow liquid will then become colourless, and is fit for de- 
positing. This solution is suitable for depositing upon 
copper or its alloys, but not upon zinc, tin, or lead, because 
they decompose it or platinise themselves in it by simple 
immersion. The liquid is used hot, and requires a strong 
battery current. As an anode of platinum would not be 
corroded in such a liquid, the solution will of course be 
gradually deprived of its metal by the process of deposition 
unless some of the chloride be occasionally added. 

A solution made by dissolving the chloride of platinum 
in one of cyanide of potassium, in the proportion of about 
twenty pennyweights of the metal to one gallon, has also been 
employed. It is used warm with a feeble current, but it also 
has the disadvantage of not dissolving the anode, and there- 
fore requires a stronger electric current, as well as renewal of 
platinum salt. 

Other solutions, composed of the double chloride of 
platinum and sodium ; or of this salt dissolved in a solution 
of oxalic acid, and made strongly alkaline by means of 
caustic soda, have been recommended, but it is difficult to 
obtain reguline white platinum from them. 

Bdttger states that for platinising he takes a boiling so- 
lution of the ordinary chloride of platinum and chloride of 
ammonium, to which he adds a few drops of solution of 
ammonia. The solution contains very little metal, and re- 
quires to be occasionally supplied with fresh metallic solution 
(' Pharmaceutical Journal,' vol. hi. p. 358). 

In my experiments, a platinum anode in pure dilute 
hydrofluoric acid of 10 per cent, was not corroded by the 
passage of a current from either six Smee's or six Grove's 
cells during many hours. Very free conduction took place ; sl 
powerful odour of ozone, and a gas which re-ignited a red-hot 
splint was evolved at the anode, but no deposit of platinum 
occurred. A solution of pure fluoride of potassium gave pre- 
cisely similar effects. 



Electrolysis of A nhy droits Hydrofluoric A cid. 1 2 1 

Also with a current from twenty-four pairs of magnesium 
and platinum, excited by a solution of one and a half ounce 
of common salt dissolved in fifty ounces of water, and the 
current passed through pure dilute hydrofluoric acid of 40 
per cent, gas was evolved from both electrodes of platinum, 
but no corrosion of the anode took place in eighteen hours. 
I also electrolysed pure hydrofluoric acid, containing 80 per 
cent, of the anhydrous acid, with platinum electrodes and a 
current from ten Smee's cells. Abundant conduction and 
evolution of hydrogen and ozone occurred ; the anode cor- 
roded and lost 16*58 grains in weight during thirty-six hours, 
and became covered with a blackish crust which partly dis- 
solved in the liquid to a brownish solution, but no electro-de- 
posit of platinum occurred. I further electrolysed anhydrous 
hydrofluoric acid in a similar way with platinum electrodes 
to that described with palladium (p. 116); with a current 
from forty Smee's elements the anode corroded rapidly, 
but did not dissolve in the liquid ; it acquired a dark red- 
brown crust, which rapidly deliquesced in the air, and 
formed a blood-red liquid, also some basic salt, by solution 
in water. 

I electrolysed during sixteen hours pure dilute hydro- 
fluoric acid of 30 per cent, mixed with an equal volume of 
nitric acid ; gases were freely evolved, but scarcely any plati- 
num dissolved, and none was deposited. Also, when mixed 
with an equal volume of strong hydrochloric acid, hydro- 
gen and chlorine were evolved, but in four hours the anode 
was but little corroded. When mixed with an equal 
volume of sulphuric acid, after many hours' action, the anode 
corroded very slowly. And with much selenious acid dis- 
solved in it, selenium containing traces of platinum was 
freely deposited, and gas was evolved as before. With 
phosphoric anhydride dissolved in it, the anode was 
slowly corroded, and gas was evolved (See ' Philosophical 
Transactions of the Royal Society,' 1869, p. 200). 

By electrolysing fluoride of potassium or of lithium in a 



122 The A rt of Electro-Metallurgy. 

melted state, a platinum anode was rapidly dissolved, and 
the resulting salt of platinum simultaneously decomposed, 
and its metal set free : and by electrolysing pure double 
fluoride of hydrogen and potassium, in a fused state, the 
platinum anode was rapidly dissolved, and imparted a colour 
to the fused salt. The fused fluorides of silver, copper, lead, 
manganese, uranium, or the fused silico-fluoride of potas- 
sium, electrolysed by a current from six Smee's elements, 
did not corrode the platinum anode. 

12. Gold. — Elec.-chem. eq. = -5 = 49*15. The 

commonest salt of gold is the terchloride ; and this is the one 
from which other salts of the metal are usually prepared. In 
addition to this one, there have been used for electro- 
depositing purposes, the oxide, bromide, iodide, sulphite, 
hyposulphite, cyanide, and double cyanides. 

Finely-divided gold is also sometimes employed in 
electro-metallurgical operations ; it is precipitated by adding 
a clear solution of protosulphate of iron (green vitriol) to a 
warm solution of chloride of gold, until it ceases to produce 
a cloud. It is a brown powder, which assumes the metallic 
lustre on being burnished. One part of gold requires about 
five parts of the crystallised sulphate to precipitate it. Oxalic 
acid produces a similar precipitate of gold. A solution of 
sulphurous anhydride (sulphurous acid H 2 S0 3 ), or a current 
of the gas, also precipitates the gold completely as metal. 
Many organic substances, if wetted with a solution of chloride 
of gold, reduce it to metal, and hence one's fingers, paper, 
wood, a feather, calico, linen, &c, become stained of a purple 
colour by contact with the liquid and subsequent exposure 
to light. 

Preparation of gold salts. — Terchloride of gold is formed 
by dissolving metallic gold in a warm mixture of one measure 
of nitric acid, and from two to three measures of hydrochloric 
acid ; the mixture is called aqua-regia. The gold dissolves 
slowly with evolution of gas ; when it is all dissolved, eva- 



Preparation of Salts of Gold. 123 

porate the solution by gentle heat, with stirring, until it is 
reduced to a small bulk, and solidifies on cooling • the residue 
should be entirely soluble in water. If it contains a white 
substance which will not dissolve, it is chloride of silver, 
derived from traces of silver in the metal * if there is a small 
amount of yellow or brown residue, some of the salt has 
been overheated ; such residue should be redissolved in a 
little aqua regia, and evaporated to dryness again. One 
ounce of gold, if it is in small fragments, or thin sheet, will re- 
quire about four ounces of aqua-regia to dissolve it. Chloride 
of gold is a yellow salt and dissolves in one and a half 
its weight of water. If it is properly made it contains one 
atomic weight (=196*6 parts) of gold and three atomic 
weights (= 106*5 parts) of chlorine, and its composition is 
represented by the formulae AuCl 3 . One troy ounce of gold 
will make 1 oz. 164^ grains of the chloride. 

Oxide of gold is obtained by digesting a solution of the 
chloride with an excess of calcined magnesia, washing the 
precipitate first with dilute nitric acid, and then with water 
only ; if caustic potash or soda be used instead of magnesia 
the oxide is liable to contain some of the alkali. 

The terbromide of gold may be formed by digesting 
oxide of gold in hydrobromic acid, and evaporating the 
solution by a gentle heat, with stirring, until it solidifies on 
cooling. 

The oxide of gold forms on addition of aqueous ammonia 
or of solutions of carbonate sulphate, or chloride of am- 
monia, a dark olive-brown substance, called fulminate of 
gold, aurate of ammonia, or ammoniuret of gold. The same 
substance is also formed on adding ammonia, or a solution 
of a salt of ammonia, to a solution of terchloride of gold. 
It is an extremely dangerous substance when dry, and detonates 
with the least friction or percussion. To form ammoniuret 
of gold, which is sometimes used in electro-gilding baths, 
convert ten parts by weight of gold into the solid chloride. 
Dissolve that salt in water, and add to the solution fifty parts 



1 24 The Art of Electro- Metallurgy. 

by weight of the strongest aqueous ammonia, and stir the 
mixture, an abundant precipitate of the ammoniuret, other- 
wise called fulminate of gold, is produced in the form of a 
yellowish brown powder. When it has subsided, pour off 
the supernatant liquid, and fill up again with water, and re- 
peat this several times, until the precipitate no longer smells 
of ammonia. The water contains a little gold, and is reserved 
for recovery of that metal. As the yellow-brown precipitate, 
when in a dry state, Is highly explosive, it should never be 
allowed to get dry, and ought not to be prepared until the 
time of forming a gilding solution with it. Particles of it 
also should not be allowed to dry upon the edges of the 
vessels nor upon filters through which the wash-liquids have 
been passed. To remove the solid salt from articles, we 
may dissolve it in a solution of cyanide of potassium. 
Freshly precipitated wet oxide of gold dissolves in a solution 
of caustic potash, to form aurate of potassium ; the solution 
is yellow, and may be employed for electro-gilding. 

Sulphide of gold is obtained by passing a current of sul- 
phuretted hydrogen gas through a solution of chloride of 
gold, as long as a precipitate occurs ; it is a blackish-brown 
powder. 

' Cyanide of gold is formed by cautiously adding a solu- 
tion of cyanide of potassium in six parts of water, to a 
neutral solution (i.e. not containing any free acid) of ter- 
chloride of gold, as long as a yellow precipitate settles down ; 
if more cyanide of potassium is added the precipitate be- 
comes dirty yellow, and is more quickly deposited ; a still 
larger quantity renders it orange yellow and redissolves it. 
It is a crystalline powder, permanent in the air ; by ignition 
it is resolved into gold and cyanogen gas ; it is not decom- 
posed by sulphuric, hydrochloric, or nitric acid, or by aqua- 
regia, unless freshly precipitated, and then only slowly. It 
is not decomposed by sulphuretted hydrogen ; hydrosulphate 
of ammonia dissolves it slowly but completely, forming 
a colourless solution, from which, by the addition of acid, 



Purity of Electro-deposited Gold. 125 

sulphide of gold is precipitated. It dissolves in aqueous 
solution of ammonia, hyposulphite of soda, or alkaline 
cyanides, but not in water, alcohol, or ether.' 

' Gold precipitated from a solution of chloride of gold by 
protosulphate of iron, dissolves in a boiling solution of 
cyanide of potassium ; a hot solution of cyanide of potassium 
will also dissolve ordinary metallic gold if air be present. 
Both oxide of gold and aurate of ammonia dissolve com- 
pletely in a solution of cyanide of potassium, and form double 
cyanide of gold and potassium. Cyanide of gold requires 
twenty-three parts of cyanide of potassium dissolved in water 
to dissolve it. For every one part of gold to be dissolved 
by the battery-process, six parts of cyanide of potassium, 
dissolved in two to four times the quantity of water at ioo° 
Fahr., is required ; two electrodes of gold being connected 
with a suitable battery, and immersed in it, until the 
required quantity of gold is dissolved.' 'The crystallised 
cyanide of gold and potassium dissolves in seven parts of cold 
and in half a part of hot water ' (Himly), ' in four parts of cold 
and in o - 8 part of hot water' (Glassford and Napier). ' It 
dissolves very sparingly in alcohol. Its aqueous solution gilds 
copper and silver by simple immersion, especially if hot, and 
the copper and silver dissolve in it.' 

A gold anode was speedily dissolved in dilute hydro- 
chloric acid, or in a saturated solution of chloride of barium, 
sodium, or ammonium, by a current from twelve Wollaston's 
cells ; but most rapidly in the sodic chloride. It was also 
slowly dissolved in a solution of chlorate of potassium, by a 
current from twenty such cells (H. Bartlett, ' Chemical News,' 
vol. xvi. p. 257). Runspaden has also shown that a gold 
anode in dilute sulphuric acid is considerably oxidised, and a 
definite hydrated oxide of gold formed (' Chemical News,' vol. 
xx. p. 179). 

Electro-deposited gold is not necessarily pure, because 
other metals are often thrown down with it, in order to obtain 
the particular shade of colour required ; for instance, white 



1 26 The A rt of Electro-Metallurgy. 

and green gold contain silver, red gold contains copper, and 
pink gold contains both copper and silver. 

Electrolysis of fluorides with a gold anode. — I electrolysed 
pure, dilute hydrofluoric acid with a gold anode and a plati- 
num crucible cathode, during many hours, with a current 
from six Smee's elements. Conduction was copious, and 
much gas was evolved from each electrode, and an odour of 
ozone came from the anode. In a few hours the anode 
became covered with a red-brown film, which did not dissolve 
but fell off. The liquid remained colourless, and was not 
discoloured by addition of sulphuretted hydrogen water to it. 
No deposit of gold occurred upon the cathode. I also 
electrolysed some stronger pure hydrofluoric acid with the 
same battery current, and also with a current from fifty pairs 
of magnesium and platinum, excited by a dilute solution of 
common salt, and obtained similar effects. The deposit upon 
the anode appeared to be metal, because it was insoluble 
in nitric acid, and looked like gold on being burnished with 
agate. 

Pure anhydrous hydrofluoric acid at io° Fahr. would not 
transmit any current from ten Smee's elements and a large 
gold anode ; but with forty Smee's cells, as in the experiment 
with palladium (see p. 116), it conducted very feebly, and, by 
continuing the action for one and a half hour, the anode ac- 
quired a dark reddish-brown film, and a few crystals, at first of 
a green colour, appeared upon its edges ; the crystals became 
yellow and then red by exposure to the air. 

A solution of pure fluoride of ammonium, containing free 
ammonia and a gold anode, conducted freely the current 
from six Smee s elements. Much gas was evolved from the 
anode, and a bright lemon-coloured powder, insoluble in 
the liquid, formed upon the anode. No deposit of gold 
occurred. 

I also electrolysed pure fluorides of lithium and potassium 
in a melted state, with a gold anode, and a current from both 
three and six Grove's elements. The anode was very rapidly 
corroded, and metallic gold separated. 



Deposition of Gold by Simple Immersion. 127 

Solutions for gilding. — There are many solutions for 
electro-gilding, some being formed by chemical means, and 
some by the separate current or battery process ; but the best 
for thick deposits are those formed with pure cyanide of 
potassium and cyanide of gold, either by the battery process 
or by chemical means. 

Separate gilding solutions are kept for different purposes, 
some for gilding by simple immersion process, and some by 
separate current ; others for gilding pale, yellow, pink, &c. 
Some are employed cold, and others hot ; some for gilding 
iron, steel, and the baser metals in general. 

Deposition of gold by simple immersion (see p. 77). — Acid 
solutions of gold deposit their metal upon surfaces of phos- 
phorus, silver, mercury., copper, and nearly all the base and 
brittle metals, by simple contact with those substances. Ac- 
cording to Commaille, magnesium deposits pure gold from an 
aqueous solution of the terchlonde (' Chemical News/ vol. 
xiv. p. 188). I have observed that crystals of silicon did not 
deposit gold from a solution of its terchloride, but that by 
contact of the terchloride in aqueous solution with benzine, 
' petroleum ether,' amylene, and a number of other liquid 
hydrocarbons, films of metallic gold gradually separated. 

For gilding articles of copper, bronze, or brass, by sim- 
ple immersion, the following solution of Roseleur's may be 
used. Dissolve 800 parts by weight of pyrophosphate of 
soda in 10,000 parts of distilled water, and add eight parts of 
strong hydrocyanic acid. Convert ten parts by weight of 
gold into soluble dry chloride, dissolve it in a reserved por- 
tion of the water to which nothing has yet been added, and 
mix the resulting liquid with the cold solution of pyrophos- 
phate. The mixture is used hot ; it is yellowish, but must 
become colourless when heated ; if it becomes red, a little 
prussic acid must be added, with stirring, until the liquid is 
colourless. If too much of the acid is added it will prevent 
the articles becoming gilded, and this may be corrected by 
adding a small quantity of chloride of gold solution. The 



128 The A rt of Electro- Metallurgy. 

articles to be gilded must be previously dipped in a very dilute 
solution of nitrate of mercury ; and whilst being gilded they 
must be kept in continual motion. To gild most success- 
fully by this process, the articles should receive a first coating 
of gold in a nearly-exhausted solution of the same kind, a 
second in a less exhausted one, and a third in a more 
freshly-prepared one, to impart a proper colour. The 
gilding occupies only a few seconds in each bath. To ob- 
tain ' green ' and ' white ' gilding in such a liquid, a solution 
of nitrate of silver is added, drop by drop, with stirring, 
until the desired colour is obtained ; before gilding green or 
white, it is best to gild the articles yellow, then dip them 
quickly in the nitrate of mercury solution, and then into the 
bath containing the nitrate of silver. 

Gilding by simple immersion is also employed for putting 
an exceedingly thin deposit of gold upon large articles of 
bronze previous to proper gilding ; then with a thicker deposit 
in a cyanide solution by the battery process. The solution em- 
ployed is composed of 180 parts of caustic potash, twenty parts 
of carbonate of potash, and nine parts of cyanide of potas- 
sium, dissolved in iooo parts by weight of water, in which 
has been previously dissolved as much chloride of gold as is 
formed from one part by weight of the metal. The mixture is 
used nearly at a boiling temperature. The artic'es to be 
gilded do not require to be previously dipped in a mercurial 
solution. As the solution loses its gold, chloride of gold 
must be added, but after four or five such additions the 
other salts must also be added with it, in the above propor- 
tions. The solution may thus be kept in order for any length 
of time. 

It is possible to gild copper and brass articles perfectly 
by simple immersion, by employing the artifice of ' quicking ' 
the surface before each immersion, by dipping it alternately 
into a solution of nitrate of mercury and into the gilding 
liquid ; and this plan is often adopted with large articles. It 
is said that copper may be gilded so perfectly by this method 



' Water-Gilding' Process. 129 

as to resist for several hours the corrosive action of concen- 
trated acids. The secret of the action is, that each film of 
mercury, being electro-positive to the gold, dissolves in the 
auriferous solution, and deposits a film of gold in its place 
(see pp. 77, 80). 

A solution for gilding by simple immersion was at one 
time extensively used by Messrs. Elkington. It was prepared 
as follows : — Convert one part of gold into terchloride, and 
expel all excess of acid; dissolve it in a small amount of 
water, and add gradually to it thirty- one parts of acid car- 
bonate of potassium ; then mix the liquid with a solution of 
thirty parts more of the acid carbonate dissolved in 200 parts 
of water, and boil the mixture for two hours. During the 
boiling the yellow solution becomes green, and is then ready 
for use. The previously cleaned trinkets of brass or copper 
are immersed for about half a minute in the hot liquid. To 
gild articles of german-silver, silver, or platinum, in this 
bath, they must be immersed in contact with wires of copper 
or of zinc. Chlorate of potash is formed in the solution by 
the gilding process, and a black powder is precipitated, con- 
taining carbonate of copper and a little purple of Cassius 
(see Miller's 'Chemistry,' vol. ii., 3rd ed., p. 814). 

The two following liquids have also been used for gilding 
by the simple immersion or ' water-gilding ' process. Con- 
vert five troy ounces of gold into chloride ; dissolve it in 
four gallons of distilled water, add twenty pounds of pure 
bicarbonate of potassium, and boil it during two hours. The 
articles to be gilded are immersed in the warm liquid from a 
few seconds to one minute, according to the degree of quick- 
ness of the action. For gilding articles of silver : dissolve equal 
weights of corrosive sublimate and sal-ammoniac in nitric 
acid, add some pure grain gold to it, evaporate the liquid to 
half its bulk ; and apply it whilst hot to the surface of the 
silver article. 

C. D. Braun gilds zinc, by immersing it in a solution of 
sulphide of gold dissolved in a solution of sulphide of am- 

K 



1 30 The A rt of Electro-M etallurgy . 

monium, excluded from the atmosphere (' Chemical News,' 
vol. xxix. p. 230). W. Kirchmann gilds clean iron by first 
applying to it sodium amalgam, which coats it with mercury. 
He then applies to the mercurialised surface a strong solu- 
tion of chloride of gold ; and finally heats the object to red- 
ness m a muffle (' Chemical News,' vol. xxvii. p. 268). 

Gilding by contact with zinc. — Joseph Steele's patent, 
dated Aug. 9, 1855. It consists substantially in im- 
mersing the articles to be gilt, in connection with a piece of 
zinc, in a hot solution, formed by adding chloride of gold to 
a solution of cyanide of potassium. It is not an economical 
process, because much of the gold is deposited upon the zinc. 

Sohaio?is for gilding by ??ieans of a separate current 
(see p. 89). — The electric current employed is usually de- 
rived either from a Bunsen's battery, or a Clamond's thermo- 
electric pile, that from a magneto electric machine being 
found to be less suitable. Many solutions have been tried, 
but none have succeeded like the double cyanide of gold 
and potassium. They may be formed either by chemical 
methods, or by means of the battery process. 

A solution may be formed by chemical means as follows. 
Convert a weighed quantity of gold into solid chloride, dis- 
solve it in water, then add a solution of cyanide of potassium 
to it as long as, but no longer than, it produces a precipitate, 
stirring the mixture on each addition, and allowing it to sub- 
side. As it is difficult and tedious to hit the exact neutral 
point, and an excess of either chloride or cyanide causes 
some gold to remain in solution, the wash-waters must be 
carefully preserved, and the gold in them recovered. When 
the neutral point is attained, allow the precipitate to subside, 
pour off the clear liquid, and fill up with water again, again 
allow to subside, and so on five or six times ; then pour the 
sediment into a filter, and complete the washing by addi- 
tion of water, and allow it to drain thoroughly. The pre- 
cipitate should not be allowed to dry because it is liable to 
contain a little fulminate of gold, derived from ammonia 



Solutions for Gilding. 131 

produced from cyanate of potash present in the cyanide. The 
wet substance should now be added to a small quantity of 
a strong solution of cyanide of potassium, and just sufficient 
additional cyanide of potassium added with stirring, to dis- 
solve the whole, a note being kept of the amount of cyanide 
consumed. About one-fifth or one-fourth more of cyanide 
of potassium should now be added, and dissolved to con- 
stitute what is termed 'free cyanide ; ' and sufficient water 
be added, with stirring, to form a solution containing the re- 
quisite amount of gold per gallon. The total amount of 
cyanide required will depend upon the quality of that salt, 
which is very variable, and with the freedom or otherwise of 
the gold salt from an excess of acid. Instead of dissolving 
cyanide of gold in the cyanide of potassium, the oxide, the 
ammoniuret, or even the chloride of gold may be added, 
and will be converted into cyanide and dissolve, if sufficient 
cyanide of potassium is present. But the disadvantage of 
this method is, that these salts of gold introduce impurities 
into the liquid; the chloride is the most objectionable, be- 
cause it leads to the formation of chloride of potassium, 
which interferes with the perfect working of the solution. 

The proportions of cyanide of gold, cyanide of potas- 
sium, and water, in an electro-gilding liquid, may vary very 
greatly without detriment to the process, as will be perceived 
from the varied proportions used by different persons. A 
very good proportion is an ounce of gold, sixteen ounces of 
cyanide of potassium, and one gallon (=160 ounces) of water, 
or an ounce of gold converted into cyanide, seven or eight 
ounces of cyanide of potassium, and 100 ounces of water ; or 
four ounces of gold, thirty-two ounces of cyanide, and 160 
ounces of water. The proportion of gold in solutions used 
by the separate current process, in large electro-gilding 
establishments, varies as much as from ten pennyweights to 
fifty troy ounces per gallon. Moderately dilute gilding solu- 
tions yield a better quality of metal, though at a slower rate, 



than stronger ones. 



k 2 



132 The A rt of Electro -Metallurgy. 

Gilding solution of M. De Ruolz — 'Dissolve ten parts of 
cyanide of potassium in 100 parts of distilled water; filter 
the liquid and add one part of cyanide of gold, prepared 
with care, well washed, and dried out of the influence of 
light ; keep the mixture in a closed glass vessel at the 
temperature of 6o° to 77 Fahr. for two or three days, out of 
the presence of light, with frequent stirring.' 

Formula of M. f. L. — ' First, take thirty-one grammes 
(see p. 381) and twenty-five centigrammes of oxide of gold, 
five hectogrammes of cyanide of potassium, and four litres 
of water, and boil them together half an hour. The re- 
sulting solution must be worked hot, and may be used to 
gild copper, brass, and silver.' 

' Second, dissolve ten parts of ferro-cyanide of potassium 
and one part of dry terchloride of gold in 100 parts of water ; 
oxide of iron will be precipitated. Boil the solution two or 
three hours in a porcelain or glass vessel, until a precipitate 
collects at the bottom, and the supernatant liquid is trans- 
parent, and of a canary-yellow colour ; filter the solution and 
dilute it with three times its volume of water.' 

M. DeBria?ifs process. — ' Dissolve thirty-four grammes of 
gold in aqua-regia and evaporate the solution until it becomes 
neutral chloride of gold ; then dissolve the chloride in four 
kilogrammes of warm water, and add to it 200 grammes of 
magnesia ; the gold is precipitated. Filter and wash with 
pure water, digest the precipitate in forty parts of water mixed 
with three parts of nitric acid to remove magnesia, then 
wash the remaining oxide of gold with water until the 
wash-water exhibits no acid reaction with test-paper. Next 
dissolve 400 grammes of ferro-cyanide of potassium and 100 
grammes of caustic potash in four litres of water, add the 
oxide of gold, and boil the solution about twenty minutes. 
When the gold is dissolved there remains a small amount of 
iron precipitated, which may be removed by filtration, and the 
liquid, of a fine gold yellow colour, is ready for use ; it may 
be employed either hot or cold.' 



So hit ions for Gilding. 133 

M. BecquereVs gilding liquid. — ' Dissolve one part of 
terchloride of gold and ten parts of ferro- cyanide of potas- 
sium in 100 parts of water ; filter the liquid to remove the 
separated iron ; add 100 parts of a saturated solution of 
ferro-cyanide of potassium, and dilute the mixture with once 
or twice its volume of water. In general the tone of the 
gilding varies according as this solution is more or less di- 
luted ; the colour is most beautiful when the liquid is most 
dilute, and most free from iron. To make the surface appear 
bright it is sufficient to wash the article in water, acidulated 
with sulphuric acid, rubbing it gently with a piece of linen 
cloth.' 

M. LevoPs solution for gilding silver. — ' Dissolve neutral 
chloride of gold in water, then add an aqueous solution of 
sulpho-cyanide of potassium, until the precipitate first formed 
is re-dissolved. The liquid will retain a slightly acid reaction ; 
if it has lost it, it must be renewed by adding a few drops of 
hydrochloric acid.' 

Gilding liquids by M. Fizeau. — First, dissolve one part of 
dry chloride of gold in 160 parts of distilled water ; then add, 
little by little, a solution of carbonate of potash in distilled 
water, until the liquid begins to become cloudy. We may 
use this liquid immediately. And, second (used by M. Lere- 
bour), dissolve one gramme of chloride of gold and four of 
hyposulphite of soda, in one litre of distilled water.' 

Mr. Wood's gilding solution. — ' Dissolve four troy ounces 
of cyanide of potassium and one of cyanide of gold in one 
gallon of distilled water, and use the solution at about 
90 Fahr. with a current from at least two cells.' 

Making gilding solutions by the battery process. — Excellent 
solutions for gilding may be made by this method ; and if 
the quantity of liquid required is not very large, this plan 
is by far the most convenient and simple one, and is un- 
attended by the risk of loss of metal, which occurs in the pro- 
cesses of solution and precipitation of gold by chemical 
means. To prepare a cyanide gilding solution by this plan, 



1 34 The A rt of Electro- Metallurgy. 

simply dissolve some cyanide of potassium in hot distilled 
water, in an earthenware vessel, in the proportion of from 
one to two pounds to each gallon. Immerse two large 
electrodes of pure sheet gold in the liquid, and pass the cur- 
rent from about three Smee's, or two Daniell's cells, stirring 
the liquid occasionally, until a clean and bright cathode of 
german-silver (substituted a short time for the gold one) re- 
ceives a proper coating. The liquid should be kept at a 
temperature of about 150 Fahr. during the process, by im- 
mersing the vessel containing it in an outer vessel of hot 
water with a lamp beneath. The quantity of gold dissolved 
from the anode is ascertained by weighing, and is not of 
material consequence, provided the deposit is good. In this 
process a portion of the cyanogen from the cyanide unites 
with the gold, and leaves potash in the solution, and after 
a time, being exposed to the atmosphere, absorbs carbonic 
acid, and thus brings carbonate of potassium into the liquid, 
but the presence of this salt is not objectionable. A very 
good gilding solution made by this method consisted of 
one gallon of water, one and a half pound of cyanide of 
potassium, and fifty pennyweights of gold. 

Gold anodes should be suspended in the liquid, either by 
gold wires protected by tubes of gutta-percha, india-rubber, 
or glass (see p. 171), or by means of platinum wires, because 
the gold is liable to be cut through by electro-chemical 
action at the surface of the liquid. 

Cold electro-gilding solutions for the separate current process. 
— Gilding in cold solutions is usually employed in cases where 
the objects to be gilt are massive, such as chandeliers, clocks, 
&c, which would otherwise require large volumes of liquid to 
be heated. Both bright and dead gilding in cold liquids is 
practised in large electro-gilding establishments. The arti- 
cles to be gilded are coated with a film of brass or copper 
by electro-depositing process, before gilding them in a cold 
solution. With a good solution the gilding is quickly effected. 

The following is the composition of cold gilding solutions 



Solutions for Gilding. 135 



I in general use, and recommended by Roseleur as giving 
- satisfactory results. 

1st Solution. 

Distilled water ...... 1000 parts. 

Aqueous ammonia . . . . . 50 ,, 

Cyanide of potassium of 70 per cent. . 30 ,, 
Gold ....... 10 ,, 

Convert the gold into solid chloride, dissolve the salt in 
water, add the ammonia with stirring ; the precipitate is 
aurate of ammonia, and highly explosive (see p. 123) ; wash it 
by decantation and subsequent filtration ; preserve the wash- 
waters, as they contain a little gold. Dissolve the cyanide of 
potassium in nearly the whole of the water, add the solution 
to the aurate of ammonia, and stir ; the aurate dissolves 
quickly ; wash any residue of aurate into the liquid by means of 
the remainder of the water, with the aid of a feather. Boil 
the mixture about one hour to expel excess of ammonia. 

As this bath is liable to become weaker in dissolved gold 
by the process of gilding, it is replenished as follows : Con- 
vert some gold into aurate cf ammonia, add 100 parts of 
water for each ten parts of gold, and then gradually dissolve 
cyanide of potassium in the mixture until the liquid is 
colourless. A little of this latter mixture is added to the 
gilding solution as occasion requires. 

2nd Solution. 

Distilled water 1000 parts. 

Ordinary cyanide of potassium . . 30or40 ,, 
(Or, Pure cyanide of potassium . . . 20 ,, ) 
Gold 10 ,, 

Convert the gold into solid chloride, and dissolve it in 
200 parts of the water ; dissolve the cyanide in the remaining 
800 parts of water. Mix the solutions and filter if necessary. 
Boil the liquid a short time before first using it. To re- 
plenish the solution, add occasionally, as required, solid 



1 36 The A rt of Electro- Metallurgy. 

chloride of gold one part, and pure cyanide of potassium from 
one to one and a half parts, each dissolved in a little water. 

The deposit of gold from these solutions is often yellow ; 
if it is dark red or black, it indicates either an excess of gold 
in the liquid or too strong a current ; and if it takes place 
very slowly and is of a grey colour, or if one portion of a gilded 
surface becomes ungilded, whilst that nearer the anode is re- 
ceiving a deposit, it indicates either that the electric current is 
too weak, or the presence of too much cyanide of potassium. 

''Solid' deposition of gold. — A process, or branch of trade, 
termed ' solid depositing ' has gradually extended itself. It 
consists in making solid articles of gold and silver, by electro- 
deposition, upon gutta-percha or other moulds; such, for 
instance, as watch and clock faces, ornamental snuff-boxes, 
and other articles elaborately chased or engraved, or which 
have very complex or undercut ornaments upon them ; the 
expense of multiplying these by the electro-process being less 
than by the ordinary means. Mr. Alexander Parkes took out 
a patent dated March 1 841, for a solution for depositing solid 
articles in gold ; it is formed thus : — Dissolve one ounce of 
pure gold in aqua regia, and evaporate the solution to dryness ; 
then add two gallons of water and sixteen ounces of cyanide 
of potassium, and work the resulting liquid at a temperature 
of about 120 or 130 Fahr. 

Gilding in hot solutions by separate current process. — This 
is the best method of gilding in the great majority of cases. 
For rapid gilding of small articles of silver, copper, bronze, 
or brass, Roseleur employs a solution composed of — 

Distilled water 1 000 parts. 

Crystallised phosphate of sodium . . 60 ,, 

Bisulphite of sodium . . . ... 10 ,, 

Cyanide of potassium (pure) ... I part 

Gold 1 „ 

The phosphate of sodium is dissolved in 800 parts of the 
water made hot. The bisulphite of sodium and cyanide of 



Gilding hi Hot Solutions. 137 

potassium are dissolved together in 100 parts of the water. 
The gold is converted into solid chloride, and dissolved in 
the remaining portion of water, and the solution poured 
slowly, with constant stirring, into the cold one of phos- 
phate of sodium ; and into this mixture, which is greenish 
yellow, is at once poured the solution of bisulphite and 
cyanide. The entire liquid soon becomes colourless, and 
is then ready for use. If the solution of phosphate is not 
cold, some of the gold is precipitated as a metallic powder. 
If the articles to be gilded are composed of iron or steel 
and require to be gilded directly, i.e. without previously 
coating them with copper or brass, he employs a liquid 
composed of — 

Distilled water , 1000 parts. 

Phosphate of sodium . . . . . 50 ,, 

Bisulphite of sodium . .... 12\ ,, 

Cyanide of potassium (pure) ... \ part. 

Gold 1 „ 

and prepares the bath in a similar manner. 

These baths are used at a temperature which varies from 
50 to 8o° C. ; they gild rapidly, and the gilding only occupies 
a few minutes. 

In gilding articles of steel, they are, after previously 
cleaning, dipped in a very hot bath, with a powerful current 
at the commencement, and the current then gradually dimi- 
nished by raising the anode until it is nearly out of the 
liquid. 

Roseleur also employs a solution composed of — 

Distilled water 300 parts. 

Cyanide of potassium (pure) . . . 5 ,, 

Gold 1 part 

The gold is converted into solid chloride, and dissolved 
in one portion of the water, and the cyanide of potassium in 
the other portion, and the two solutions then mixed. 

This liquid may be employed at almost any tempera- 



138 The A rt of Electro- Metallurgy. 

ture, but is liable to give a yellow deposit on the upper part 
of an article, and a red one at the bottom ; and even to un- 
gild the distant parts, whilst the near parts are receiving 
a deposit. Both these defects may, however, be diminished 
by keeping the articles in brisk and continual motion. 

Coloured gilding. — To obtain red gold, add to either of the 
foregoing solutions a sufficient proportion of either of the 
acetate of copper liquids (see pp. 207, 208), or we may gild red 
in an old gilding bath in which a great many copper articles 
have been gilt, taking care to use a strong electric current 
To obtain green or white gold, add to one of these baths a 
sufficiency of either a dilute solution of argentic nitrate, or 
better, one of double cyanide of silver and potassium. To 
obtain what is called ' pink ' gold, the articles are first gilt 
yellow, and then red, and afterwards a mere blush of silver 
is deposited upon the red in a cold silver bath; they are 
finally burnished. If the proper pink colour is missed, strip 
off the coating of silver and copper, by immersing the articles 
during a few seconds in a mixture of five parts sulphuric and 
one of nitric acid (the yellow gilding then reappears), and 
try again. 

To obtain a rich deep gilding from a cyanide liquid, the 
solution should be strong, and the articles should either 
appear of a dark yellow or a rich orange colour, approaching 
to brown, on coming out of the liquid ; then, on scratch- 
brushing them, they will acquire the desired appearance. A 
very rich dead gilding may also be obtained in a cyanide 
solution, by adding a little wet aurate of ammonia to the 
liquid just before gilding. And a bright clear yellow gilding 
may be obtained by adding to an ordinary cyanide gilding 
solution a small quantity of caustic soda. If a deposit of 
gold appears of a blackish colour when coming out of the 
liquid, it will not have a satisfactory appearance imparted to 
it either by brushing or burnishing. 

Sometimes a defective colour in gilding is improved by 
immersing the article, until its colour is white, in a solution 



Coloured Gilding. • 139 

of nitrate of mercury, then volatilising the mercury by heat, 
and scratch-brushing the article. 2nd. Or dip the article in 
strong sulphuric acid, then heat it until white fumes are freely 
evolved, and immerse it at once in very dilute sulphuric 
acid. 3rd. Or make into a wet paste, with a little water, a 
mixture in powder, of two parts nitrate of potassium, one of 
sulphate of zinc, one of alum, and one of common salt, and 
smear the article with a layer of the paste ; then heat it to 
blackness upon an iron plate, over a clear fire, and plunge it 
into water. By varying the mixture, different tints of colour 
are obtained. 4th. Or smear the article with a thick magma 
of powdered borax and water, heat it until the borax 
undergoes igneous fusion, and plunge it into dilute sulphuric 
acid. 

Copper or brass trinkets, which require the gold to have 
a dead appearance upon them, are dipped for a moment in a 
mixture of equal parts of sulphuric and nitric acids, to which 
a little common salt is added. 

The colour of the deposit may also be largely regulated by 
the size of the anode. If the anode dips but slightly into 
the solution, and the deposit is then of a pale yellow colour, 
it will become full yellow with deeper immersion of the 
anode, and of a red colour if the anode is wholly immersed. 
It is also largely affected by motion of the cathode ; if the 
solution gilds of too dark a colour, keeping the article in 
motion will remedy the defect. The colour may also be 
greatly varied by depositing other metals with the gold. In 
all electro-gilding establishments alloys of gold, with silver 
and copper, are deposited, in order to obtain the requisite 
colour, and the general method adopted for regulating the 
colour of electro-gilding is as follows : — After having pre- 
pared the solution, work it with a large copper anode until 
the deposited metal begins to deteriorate in colour ; then 
replace the' copper by a small gold anode. With the copper 
anode can be obtained a full rich colour, becoming deeper 
as the temperature of the liquid is higher ; to produce a 



140 The A rt of Electro- Metallurgy. 

paler yellow, use a small gold anode with the liquid at a 
lower temperature. 

With cyanide of potassium solutions, containing various 
dissolved metals, silver goes down first by the electric-current, 
then silver plus gold, then gold alone, then gold and copper, 
then copper alone, then copper plus zinc. If salts of lead 
are added to the gilding liquid, lead will first be precipitated 
alone, and then the lead will cause the gold to be deposited 
in a bright condition. 

Necessity of free cya?iide of potassium. — In all cyanide 
gilding liquids it is necessary to add much more cyanide of 
potassium solution than is sufficient to dissolve all the salt of 
gold ; this excess is termed ' free cyanide.' The proportion 
of free cyanide employed by different electro-gilders varies 
somewhat, but does not exceed certain limits, otherwise the 
liquid will not work well ; from one-fourth to one-half of 
the quantity required to dissolve the salt of gold is a usual 
proportion. If too much free cyanide is employed the 
gilding is apt to assume what is termed a 'foxy ' appearance, 
the anode also is dissolved whilst the current is not passing, 
and the solution is more prone to decompose and become of 
a dark colour. The reason why free cyanide is necessary in 
gilding operations, is because the cyanide liberated from its 
gold at the cathode, requires some time to get across the solu- 
tion to the anode, and meanwhile the anode must be sup- 
plied with some, in order to render soluble the cyanide of 
gold formed upon it. The actual quantity of cyanide of 
potassium required, both to dissolve the gold salt, and to 
form free cyanide, differs very greatly, because the quality of 
commercial cyanide is very variable. The larger the pro- 
portion of actual cyanide present in the salt, the smaller 
the proportion of the salt necessary both to dissolve the gold 
salt and to form free cyanide. It must not be forgotten 
that commercial cyanide is liable to contain from about 30 
to 98 per cent, of actual cyanide, and that all the other salts 
in it are almost useless as solvents of gold, and some of 



Management of Gilding Solutions. 1 4 1 

them are positively detrimental to electro-gilding opera- 
tions. 

Management of electro-gilding solutions. — Cyanide gild- 
ing solution is generally contained in a glazed iron vessel, 
and heated either by a stove or by gas-jets beneath ; or it is 
contained in a stoneware or glass pan immersed in boiling 
water. On account of the usual smallness of the articles to 
be gilded, the thinness of the deposit, and the rapidity of 
the action in a hot liquid, the objects only require to be 
immersed in the solution for a few minutes ; when a thicker 
deposit is desired, in order to maintain a proper condition 
of deposit, they should be taken out several times, brushed, 
and re-immersed. The strength of battery used for gilding 
is generally about two Bunsen's cells, of different sizes, 
according to the magnitude of the articles to be gilded. The 
loss of water by evaporation is generally made good by 
adding a little distilled water, after having finished gild- 
ing. 

Gilding done in hot solutions, is superior in several re- 
spects to that done in cold ones. The deposits are smoother 
and cleaner, and, what is more important, the same thickness 
of deposit is more durable when made in a hot liquid than 
when effected in a cold one. This may be partly explained 
by the fact that in the subsequent cooling the pores of the 
film of metal contract. Gilding done in hot solutions is also 
generally more uniform, and of a deeper or richer colour 
than that done in cold ones. 

Cyanide gilding solution deteriorates by long-continued 
working, in consequence of silver getting into it from the 
anodes, and depositing with the gold, gradually increasing 
its paleness of colour. Gold may be obtained in a pure state 
from impure anodes, &c. by dissolving the anode in mercury 
(seep. 358) ; then immersing the amalgam in warm dilute nitric 
acid ; this will gradually dissolve all mercury, silver, copper, 
and lead, and leave the gold in a state of fine metallic powder. 
Before adding the amalgam to the acid, the excess of mercury 



T42 The A rt of Electro-Metallurgy. 

may be removed by squeezing it through wash-leather, but a 
little of the gold passes through also. 

In all cyanide solutions, and especially in those contain- 
ing a large excess of cyanide of potassium, and exposed to 
heat and sunlight, a small portion of the alkaline cyanide is 
continually being transformed, by contact with the air, into 
carbonate of potassium and cyanide of ammonium. To 
remedy this, most electro-gilders add occasionally a small 
quantity of cyanide of potassium to the liquid, others add a 
little hydrocyanic acid; the latteris rather themore suitable, 
because it re-converts the carbonate into cyanide, but it has 
the disadvantage of containing only about 5 per cent, of the 
acid, and of being a deadly poisonous liquid, and requiring 
to be kept in a dark and cool place. 

Cyanide gilding liquids are also liable to vary in com- 
position, in consequence of the quantity of gold deposited 
being sometimes greater and sometimes less than that dis- 
solved ; if it is greater, the cathode liberates an excess of free 
cyanide, and if it is less, the reverse. The gold anode 
should always appear clean ; if it has a crust upon it there is 
a deficiency of cyanide, but if it is black and has a slimy 
appearance, and especially if it evolves gas, the solution is 
deficient of gold ; this may be remedied by employing for a 
time a very large anode and a small receiving surface. By 
attending properly to the indications, a cyanide gilding 
solution may be used for any length of time. 

Gilding base metals. — Before gilding articles composed of 
antimony, lead, tin or zinc, Britannia metal, pewter, type metal, 
&c. it is better to coat them with a film of copper or brass, in 
a cyanide solution, or to begin the gilding in a hot and nearly 
exhausted gold bath, and to carefully scratch-brush them. 

A weaker solution is recommended for gilding articles 
of iron or steel than for gilding copper, viz. one consisting of 
about one measure of the ordinary cyanide gilding liquid, 
and four or five measures of water containing about 1 per cent, 
of cyanide of potassium. The solution should only be 



Gilding Base Metals. 143 

moderately warm, and a feeble current employed. In gild- 
ing german-silver or brass articles, also the solution should 
be weak, and a feeble current employed, because both those 
alloys are rather strongly electro-positive to gold in a strong 
cyanide solution, and will therefore coat themselves by 
simple immersion in it, and if this action is too strong it will 
prevent the adhesion of the deposited metal. 

Previously prepared and cleaned articles of zinc, are first 
coated with a thin film of copper or brass in a warm cyanide 
solution, then * scratch- brushed,' and a thicker coating of 
copper put upon them in a cold liquid, composed of a 
mixture of ten volumes of water and one of sulphuric acid, 
saturated with sulphate of copper, and then two or three 
volumes more of water added. If the deposit of copper 
appears patchy, either the original cleaning process or the 
first coating of copper was imperfect ; and the articles must 
be thoroughly scratch-brushed, and both the coatings be 
repeated. The articles should now be ' quicked ' by rapidly 
dipping them into a solution, composed of distilled water 
1000 parts, sulphuric acid two parts, and nitrate of mercury 
one part (see also p. 323), then rinsed, and slightly silvered 
by dipping into a mixture of water 1000 parts, cyanide of potas- 
sium forty parts, and nitrate of silver ten parts. They are 
then ready for gilding by means of a current, strong at first 
so as to cover the articles quickly, and then gradually 
diminished so as to give a good deposit. 

Gilding the insides of vessels. — The insides of vessels are 
gilded, by filling the vessel with the gilding solution, suspend- 
ing a gold anode in the liquid, and passing the current. 
The lips of cream-jugs, and the upper parts of vessels of 
irregular outline, are gilded by passing the current from a 
gold anode, through a rag wetted with the gilding solution, 
and laid upon the part. 

Ungilding of articles of silver and iron. — Make them the 
anode, in a solution composed of one part of cyanide of potas- 
sium dissolved in ten parts of water. 



144 Tiie Art of Electro-Metallurgy. 

Recovery of gold fro7?i wash-waters. — Wash- water from 
gilding operations, or from the making of salts of gold, should 
never be thrown away without previously testing it in a 
proper manner. The greater the quantity of free acid, alkali, 
or alkaline salts, in such a liquid, the more capable is it 
usually of dissolving some of the gold. All such liquids 
have their gold thrown down from them completely by 
immersing in them clean plates of zinc, provided they are 
made slightly acid, and sufficient time is allowed. Water 
containing free chloride of gold, maybe perfectly precipitated 
by means of a solution of green vitriol. 

Recovery of gold front cyanide solutions} — Add an excess 
of hydrochloric acid, carefully avoiding the poisonous 
fumes of prussic acid ; heat to boiling; a yellowish-green 
precipitate forms, but some gold still remains dissolved ; cool 
the liquid, tfiis separates more of the gold. Decant or filter 
the clear portion, heat the liquid, and add some filings of zinc; 
in an hour or two, all the remainder of the gold will be precipi- 
tated. Decant the liquid, boil the residue with dilute hydro- 
chloric acid ; wash it and add it to the other portions. 
Ignite and fuse the mixture in a platinum crucible, with an 
equal weight of acid sulphate of potassium. Dissolve the 
saline residue in boiling sulphuric acid, wash it then with 
water ; perfectly pure gold will remain (R. Huber, ' Chemical 
News,' vol. viii. p. 31). 

' Cyanide of gold and potassium gilding liquid, when 
mixed with sulphuric, hydrochloric, or nitric acid, slowly de- 
posits cyanide of gold ; and when boiled with hydrochloric 
acid, it is completely resolved into cyanide of gold and 
chloride of potassium. Similar effects are produced by sul- 
phuric or nitric acid, and even by oxalic, tartaric, and acetic 
acids. When heated with sulphuric acid it gives off hydro- 
cyanic acid gas, and, after ignition, leaves a mixture of gold 
and sulphate of potassium. Iodine sets free cyanogen gas, 
forms iodide of potassium, and throws down the cyanide of 
gold. 

1 See also p. 192. 



Recovering Gold and Silver from Old Solutions. 145 

' It we pour hydrochloric acid into a pure solution of 
gold in cyanide of potassium, there is slowly formed at 
ordinary temperatures, and immediately on the application 
of heat, a yellow precipitate, which is cyanide of gold ; the 
filtered liquid which has given this precipitate still contains 
a little gold in solution. On evaporating the liquid to 
dryness, fusing, dissolving, and filtering afresh, there remains 
upon the filter the remainder of the gold. 

' Crystallised double cyanide of gold and potassium fuses 
and effervesces by heat, and is resolved into cyanogen gas, 
ammonia, and cyanide of potassium, if air be present ; its 
complete decomposition requires a strong red heat. When 
it is strongly ignited, mixed with an equal weight of car- 
bonate of potash, a button of metallic gold is obtained. 

' To obtain the remaining gold from gilding solutions 
which have become inactive, they should be evaporated to 
dryness, the residue finely powdered, and intimately mixed 
with an equal weight of litharge, fused at a strong red heat, 
and the lead extracted from the alloy button of gold and 
lead by warm nitric acid ; the gold will then remain as a 
loose, yellowish-brown, spongy mass ' (Bottger, ' J. Pr. 
Chem.' xxxvi. 169; Eisner, Redtel Hessenberg, 'J. Pr. 
Chem.' xxxvii. 477; xxxviii. 169, 256). 

Recovering gold or silver, by M. Bolley. — ' Cyanide of 
gold, dissolved in an excess of cyanide of potassium, resists 
all the means which we have tried to separate them ; and 
hydrosulphuric acid, for example, does not produce a preci- 
pitate. By the wet way we cannot always precipitate the 
gold completely, and for that reason MM. Bottger, Hessen- 
berg, Eisner, and others, propose to evaporate the liquid to 
dryness ; mix the residue with its own weight of litharge, 
fuse the mixture at a strong red heat, then dissolve the lead 
from the alloy by boiling it a long time with dilute nitric 
acid, which leaves the gold in the form of a light sponge. 

' The following process is applicable on the small scale, 
with a spirit-lamp and a crucible of platinum. Evaporate 

L 



1 46 The Art of Electro- Metallurgy. 

the solution to dryness, mix the saline mass with its own } 
weight of sal-ammoniac, and heat it gently ; ammoniacal salts ' 
decompose, as we have said, the metallic cyanides, and form 
cyanide of ammonium, which is itself decomposed by the 
heat and volatilised, whilst the acid of the ammoniacal salt 
(the body which salines the ammonia) combines with the 
metals (passed to the state of oxides), which were previously 
united to the cyanogen. The sal-ammoniac then in this case j 
forms chloride of potassium and chloride of gold, and, if the j 
salt contains ferro-cyanide of potassium, chloride of iron in ' 
addition. The chloride of gold is easily decomposed ; the f 
chloride of iron is partly decomposed, and leaves oxide of 1 
iron in beautiful crystalline spangles. The undecomposed j 
portion of the chloride of iron, like the chloride of potassium, 
may, after the decomposition is finished (which only requires j 
a low red heat), be washed away by water, leaving the I 
gold in the form of a light coherent mass, and the iron in j 
small spangles, which may be removed by mechanical means. [ 

' If we fear that a little of the gold remains mixed with | 
the iron in a pulverulent state, we may dissolve it in hot aqua 
regia, and precipitate the gold from the resulting solution by I 
adding to it a solution of protosulphate of iron ; but this , 
appears superfluous ; and I am assured, by evaporation of \ 
given volumes of the same solution of gold, the evaporation j 
and calcination of the sal-ammoniac, and other operations, 
that we have collected in a sufficiently exact manner all the j 
gold of.these solutions. 

' The same process is applicable to the solution of silver, j 
and, independently of the oxide of iron (of the ferro-cyanide ! 
of potassium), we obtain chloride of silver, which is soluble ! 
in aqueous ammonia.' 

13. Silver. — Elec. chem. eqt.=io8. As silver is the most j 
prominent metal in electro-depositing processes, I shall speak ; 
of it the most fully. The commonest salts of silver are the ! 
chloride, nitrate, oxide, cyanide, and sulphide ; the sulphite, 
hyposulphite, acetate, and other salts have however been j 



Making Salts of Silver. 147 

tried for electro-plating purposes, but the one which has best 
stood the test of experience and time is the double cyanide 
of silver and potassium. 

Most of the salts of silver are formed from the nitrate. 
The nitrate is produced by adding pure grain silver, in small 
quantities at a time, to a warm mixture of one measure of 
distilled water and four measures of the purest and strongest 
nitric acid. If the liquid is too hot, or too much silver is 
added at a time, the action will be very strong, and loss of 
materials, by boiling over of the liquid, may be occasioned ; 
in such a case add a small quantity of cold distilled water. 
When the liquid ceases to dissolve more metal, it should be 
evaporated and crystallised, or else kept in a covered vessel, 
protected from the light until required to be used. 

The oxide is obtained by adding a solution of either 
caustic potash, caustic soda, or clear lime-water, to one of 
nitrate of silver as long as it produces a precipitate, filtering 
and washing the oxide, which is a brown powder. The wash- 
water contains a little oxide of silver in a dissolved state. 
The chloride may be obtained by adding dilute hydrochloric 
acid or a solution of common salt, in slight excess, to one of 
the nitrate in a similar manner, filtering and washing the 
white flocculent precipitate, which must be kept in the dark. 
In this case the wash-waters do not contain silver, and may 
therefore be thrown away. 

Fluoride of silver may be obtained by saturating pure di- 
lute hydrofluoric acid in a platinum vessel with argentic oxide 
or carbonate, and evaporating the clear solution to perfect 
dryness. It is extremely soluble in water and easily fusible. 
The electrical relations of substances, in the fused salt I found 
to be as follows, the first-named substance being the most 
positive — silver, platinum, charcoal of lignum-vitae, palladium, 
gold ; .and in a dilute aqueous solution of the salt — aluminium, 
magnesium, silicon, iridium, rhodium, and carbon of lignuni- 
vitse, platinum, silver, palladium, tellurium, gold (' Chemical 
News,' vol. xxi p. 28). 

l 2 



1 48 The A rt of Electro-Metallurgy. 

Nearly all the salts of silver (except the sulphide) become 
converted into the cyanide by immersion in a solution of 
cyanide of potassium, and therefore the nitrate and chloride 
are sometimes used instead of the cyanide, to form with 
cyanide of potassium the plating liquid. But this is a 
bad mode of procedure, because the same amount of 
materials is used, and nitrate or chloride of potassium are 
thereby introduced into the plating liquid, and these sub- 
stances are objectionable. 

Cyanide of silver is generally prepared by adding a solu- 
tion of cyanide of potassium to one of nitrate of silver just as 
long as a precipitate occurs ; the white precipitate, which is 
cyanide of silver, is insoluble in water, and is not perceptibly 
soluble in commercial hydrocyanic acid ; it dissolves very 
freely in a solution of cyanide of ammonium, potassium, or 
sodium, and in hyposulphite of soda solution ; it is also 
soluble in solutions of ammonia, carbonate of ammonia, 
sal-ammoniac, nitrate of ammonia, and ferro-cyanide of po- 
tassium. 

Chemical characters of cyanide of silver. — According to 
Messrs. Glassford and Napier, cyanogen in the presence of 
cyanide of potassium, possesses a greater affinity than any 
other substance for silver; decomposing every salt of that 
metal except the sulphide, and forming cyanide of silver. 

In dissolving the oxide, carbonate, chloride, or ferro- 
cyanide of silver, in a solution of cyanide of potassium, 
they are all decomposed, and cyanide of silver is always 
formed. Cyanide of silver should be dried below 260 Fahr. 
Hydrochloric acid decomposes it with evolution of hydro- 
cyanic acid gas ; cold nitric acid has no action upon it ; a 
boiling mixture of sulphuric acid and water decomposes it, 
with escape of hydrocyanic acid gas, and formation of sul- 
phate of silver ; it is soluble in solutions of the alkaline 
chlorides, but its best solvent is an aqueous solution of cyanide 
of potassium, of which salt it requires one equivalent (sixty- 
five parts), to dissolve one equivalent (134 parts). The 



Electrolysis of Salts of Silver. 149 

resulting solution, when evaporated, yields crystals of double 
cyanide of silver and potassium, which are soluble in eight 
parts of cold and in one part of boiling water. The solution 
of this double salt, which is nearly the same as the ordinary 
plating solution, may be boiled for any length of time without 
being decomposed, and it is very little affected by light ; it is 
decomposed by all acids, and they precipitate the silver as 
cyanide of silver \ the hydro-acids — hydrochloric acid for ex- 
ample — decompose the cyanide of silver also ; sulphuretted 
hydrogen precipitates the silver as sulphide of silver (' Philo- 
sophical Magazine,' vol. xxv., 1844, pp. 56-71). According to 
Baup, the double cyanide of silver and potassium (K Cy, 
Ag Cy) requires for solution four parts of water, or twenty-five 
parts of 85 per cent alcohol, each at 20 C. It does not 
become discoloured by exposure to sunshine, nor make 
stains upon paper nor on the skin. The double cyanide 
of silver and sodium (Na Cy, Ag Cy) dissolves in five parts 
of water, or twenty-four parts of 85 per cent, alcohol, at 

20° C. 

Electrolysis of salts of silver. — A highly- concentrated so- 
lution of argentic nitrate, made as neutral as possible, is 
easily decomposed, and yields coherent metal by a sufficiently 
feeble current. An anode of silver is, however, indispen- 
sable (Becquerel,' Chemical News,' vol. vi. p. 126). I have 
electrolysed a solution of argentic nitrate, and obtained a 
thick, black, insoluble crust upon the silver anode ; the 
crust was probably a peroxide of silver, but it also contained 
a compound of nitrogen. Fused argentic nitrate yields silver 
at the cathode and oxygen gas at the anode. Fused chloride 
of silver is resolved into silver and chlorine. 

The sulphate of silver is too sparingly soluble, and too 
bad a conductor to be of much value in electro-plating. 
The hyposulphite is much more soluble, and has been used 
for practical purposes, but abandoned. Solutions of nitrate, 
chloride, and carbonate of silver in excess of aqueous am- 
monia have also been tried. They are good conductors, but 



1 5 o The A rt of Electro-Metallurgy. 

contain argentate of ammonia or fulminate of silver, which 
is an extremely dangerous substance when in a dry state, 
and detonates with fearful violence by the slightest friction 
or percussion. The iodide of silver and potassium, the 
acetate of silver, the sulphocyanide of silver and potassium, 
and the potassio- tartrate of silver, have all been tried for 
depositing purposes, but do not appear to equal the double 
cyanide of silver and potassium ; in the electrolysis of all 
of them there is occasionally observed a black crust, pro- 
bably containing some peroxide of silver, upon the silver 
anode. 

I have electrolysed artificially-chilled anhydrous hydro- 
fluoric acid by means of a pure silver anode, and a current 
from ten Smee's cells. The current was conducted more 
freely than with an anode of palladium, and still more so 
than with one of gold ; the anode corroded rapidly, and be- 
came covered first with some black powder upon its edges, 
and then with a grey powder (probably metallic silver) which 
contained only a trace of soluble silver salt. I also electro- 
lysed a saturated neutral aqueous solution of argentic fluoride 
with a current from six Grove's cells, a small platinum anode 
and a large platinum cathode. Free conduction occurred, 
no gas or odour was evolved, a thick, hard, and strongly ad- 
herent, black crust quickly formed upon the anode, and a 
rapid deposit of yellowish scales of silver upon the cathode ; 
the crystals soon extended upwards and united the elec- 
trodes. From the behaviour of the black crust with strong 
nitric, hydrochloric, and sulphuric acids, and also with 
aqueous ammonia ; and from its evolving, when heated to 
redness, a gas which re-inflamed a red-hot splint explosively, 
and losing nearly the theoretical proportion by weight in the 
process, and leaving metallic silver, I concluded the crust 
to be peroxide of silver (Ag 2 2 ). By the electrolysis of a 
more dilute solution a similar crust was formed, but gas was 
also evolved at the anode. 

I also made a number of experiments of electrolysing 



Deposition of Silver by Simple Immersion. 1 5 1 

argentic fluoride in a fused state with platinum electrodes, 
in a covered platinum cup, with a current from six Smee's 
elements. In each case conduction commenced before the 
salt had fused ; and when the salt was liquid the conduc- 
tion was as perfect as if the electrodes were united by a 
metal wire. No signs of genuine electrolysis could be de- 
tected in either instance. I also electrolysed the fused salt 
with a rod of highly-ignited charcoal of lignum-vitae, and a 
current from ten Smee's cells, but only a small amount of 
conduction occurred in consequence of the resistance of the 
carbon. The anode was corroded and evolved gas (See 

* Phil. Trans. Royal Society,' 1870, p. 234; ' Chemical News,' 
vol. xxi. p. 28). 

According to F. Wohler, if a current from two Bunseii's 
cells is passed through a dilute solution of sulphuric acid or 
sodic sulphate by means of a silver anode, the anode be- 
comes covered with black amorphous argentic peroxide, and 
this oxidation is due to ozone. With a solution of potassic 
nitrate similarly treated, flocculent light-brown argentic oxide 
is formed. In one of potassic ferro-cyanide, the anode ac- 
quires a film of white amorphous argentic ferro-cyanide. And 
in a solution of potassic dichromate it becomes covered 
with a reddish black film of crystallised argentic chromate 
('Chemical News,' vol. xviii. p. 189). 

The electrolysis of melted caustic soda with an anode of 
silver causes the silver to dissolve and be deposited upon 
the platinum cathode ; but, on cleaning the cathode with 
nitric acid, a black powder of platinum is left (Brester, 

* Chemical News/ vol. xviii. p. 145). I have repeatedly met 
with a similar effect with fluoride of silver melted in vessels 
of platinum. 

Depositio?i of silver by simple immersion (see pp. 77, 78). 
— Aluminium throws down the silver from acid or neutral 
solutions of argentic nitrate ; slowly in dilute solutions ; also 
immediately from solutions of chloride or chromate of silver 
in aqueous ammonia. It rapidly decomposes chloride of 



152 The A rt of Electro-Metallurgy. 

silver in a state of fusion, evolving great heat (A. Cossa, 
Watts' ' Dictionary of Chemistry,' 2nd Supplement, p. 54). 

A solution of sulphate of silver is not reduced, but one 
of argentic nitrate deposits its silver by contact with hydrogen, 
obtained by a variety of methods (Brester, ' Chemical News,' 
vol. xviii. p. 144). According to J. Spiller, electro deposited 
nickel does not deposit silver from a solution of argentic 
nitrate ('Chemical News,' vol. xxiv. p. 175). 

I have observed that hydrogen deposits silver from semi- 
fused argentic fluoride (' Chemical News,' vol. xxi. p. 28) ; 
also that carbon and crystalline boron do not separate silver 
from that salt at a red heat, nor does boron separate it from an 
aqueous solution of that salt ; that crystals of silicon thrown 
upon melted argentic fluoride become red-hot, undergo rapid 
combustion, forming fluoride of silicon and depositing silver ; 
that those crystals also deposit crystals of silver slowly from an 
aqueous solution of that salt ; and from a mixture of solution 
of argentic fluoride, hydrofluoric acid, and nitric acid, they 
liberate bubbles of spontaneously inflammable siliciuretted 
hydrogen gas ('Chemical News,' vol. xxiv. p. 291). A frag- 
ment of stannous fluoride also deposited metallic silver from 
an aqueous solution of argentic fluoride in a platinum dish. 

According to Raoult, gold in contact with silver in a cold 
or hot acid or neutral solution of a salt of silver receives no 
deposit of that metal (* Journal of Chemical Society,' vol. ii. 
p. 465). 

Silvering by simple immersion. — This process is chiefly 
applicable to small articles, such as pins, buttons, buckles, 
coffin nails, hooks and eyes, &c. where only a very thin coat- 
ing of silver is required. The following solutions, in the 
proportions indicated, are used by adding a small quantity 
of water sufficient to form the ingredients into a pasty liquid 
of the consistence of cream, stirring the articles thoroughly 
about in it, or rubbing them over with it, until they have ac- 
quired the desired degree of whiteness. 

1 st. Take equal parts of chloride of silver and bitartrate 



Silver i?ig by Simple Immersion. 153 

of potash. 2nd. Take chloride of silver one part, alum two 
parts, common salt eight parts, and cream of tartar eight 
parts. 3rd. Take chloride of silver one part, prepared chalk 
one part, common salt one and a quarter part, and pearlash 
three parts. 4th. A 'novargent' solution for resilvering old 
plated goods consists of 100 parts of hyposulphite of soda, 
and chloride or any other salt of silver, fifteen parts. Com- 
pounds of this description are also used for silvering 
clock faces, thermometer and barometer plates, and many 
other articles of copper and brass. Or one part of chloride 
of silver mixed with eighty or 100 parts of cream of tartar (bi- 
tartrate of potassium), to which may be added or not about 
eighty or 100 parts of common salt, is dissolved in boiling 
water, and the articles contained in a basket are immersed, 
and stirred about in the hot liquid. An old solution is of a 
green colour from the presence of dissolved copper, and 
works better than a new one. If there is the least particle 
of metallic zinc or iron present, it causes a red deposit of 
copper upon the articles. Another solution employed for a 
similar purpose is composed of 1000 parts of water, sixty 
parts of cyanide of pocassium, and ten parts of nitrate of 
silver ; it is used at a boiling temperature. The action of 
this bath depends upon the fact that copper is more electro- 
positive to silver in proportion to the excess of free cyanide of 
potassium present. 

The following solution of the double sulphite of silver 
and sodium, according to Roseleur, may be used cold. It 
is prepared as follows : Dissolve four parts of crystals of 
washing soda in five parts of distilled water. Pass sul- 
phurous anhydride gas (S0 2 ) through the liquid by bub- 
bling it through mercury at the bottom of the vessel to pre- 
vent the exit tube becoming clogged with crystals, until the 
liquid redissolves the crystals of bicarbonate and slightly 
reddens blue litmus paper. Set it aside for twenty-four hours 
to allow some bisulphite of sodium to crystallise out. Take 
the liquid part only, stir it well to remove carbonic acid. 



154 The Art of Electro-Metallurgy. 

Now add, if it is alkaline, some more sulphurous gas, or if it 
is acid, a little more carbonate, until the liquid after stirring 
renders blue litmus paper violet or slightly red. To the 
clear liquid add, with stirring, a solution of argentic nitrate, 
until the precipitate produced begins to be slow in dissolv- 
ing ; the solution is then ready. 

This liquid is said to be ' always ready to work, and pro- 
duces quite instantaneously a magnificent silvering upon 
copper, bronze, or brass articles, which have been thoroughly 
cleansed, and passed through a weak solution of nitrate of 
binoxide of mercury, although this last operation is not ab- 
solutely necessary.' The bath is renewed by addition of 
nitrate of silver, and sooner or later also some bisulphite of 
soda. Some of the silver of the solution deposits itself upon 
the sides of the vessel. Roseleur states that he has used 
this bath for five consecutive years, and has daily silvered in 
it ' as many articles as a man could conveniently carry, and 
at prices varying ten cents to two dollars per kilogramme,' 
and he ' does not doubt that it would eventually replace all 
the other known methods. He further states that the deposit, 
without the aid of electricity, may become nearly as thick as 
desired, and in direct ratio to the length of the immersion.' 

This particular process differs from nearly all other ones 
of metallic deposition upon metals, in being only in part an 
electrical action. When a metallic article is immersed in 
a bath of another metal, in which it coats itself, a portion of 
the immersed metal dissolves and generates an electric cur- 
rent, which decomposes the liquid, and deposits an equiva- 
lent of the other metal as a coating upon the immersed 
article ; this deposited film arrests the action, and prevents 
a thick coating being formed. But in this particular liquid 
a spontaneous chemical change also takes place ; the sul- 
phurous anhydride of the sulphite of silver takes oxygen to 
itself, to form sulphuric anhydride, and sets the silver free, 
and this silver adheres to the articles, and to the vessel con- 
taining the liquid. The sulphuric anhydride unites with 



Solutions for Plating by a Separate Current. 155 

some of the soda of the undecomposed portion of the sul- 
phite and liberates sulphurous anhydride, and forms sulphate 
and bisulphite of sodium. The process is partly like that of 
coating looking-glasses with pure silver. 

Silvering' by contact with zinc (see p. 82). — Mr. Joseph 
Steele took out a patent, dated August 9th, 1850, for silvering 
articles by immersing them in a silver solution in contact 
with a piece of zinc of proper size. The process is as 
follows : Dissolve four ounces of pure silver in twenty ounces 
of nitric acid ; also dissolve separately one and a half pound 
of common salt in one and a half gallon of water ; mix the two 
solutions together ; allow the mixture to remain until clear, 
pour away the clear liquid, and wash the precipitate, which 
is chloride of silver ; next fuse together twenty- four ounces 
of ferro-cyanide of potassium and twelve ounces of carbonate 
of potash, and, when the mass is cold, add it, together with 
the chloride of silver, to one gallon and a half of water, boil 
the mixture and filter it ; it is then ready for use. 

Solutions for plating by separate current (see p. 86). — 
These may be made either by chemical means or by the aid 
of an electric current. The best solution for general purposes 
is the double cyanide of silver and potassium, and when re- 
quired in large quantities it is usually made by chemical 
means. Many solutions have been proposed and tried for 
depositing silver by the battery process, but none have stood 
the test of time and experience like the one composed of 
double cyanide of silver and potassium dissolved in water, 
and a little free cyanide of potassium added. It must, how- 
ever, always be remembered, when making cyanide deposit- 
ing solutions with the aid of potassic cyanide, that the com- 
position of this salt as usually sold is extremely variable, and 
unless the depositor is aware of this he may be led quite 
astray in his calculations, and unwittingly introduce various 
impurities into his depositing liquids. 

Ordinary cyanide plating solution may be made of 
various strengths, from half an ounce of silver to the gallon 



1 5 6 The A rt of Electro-Metallurgy. 

of water, to two, four, six, or more ounces, and from an 
ounce of cyanide of potassium to several pounds per gallon, 
and still be effective in working. One part of silver in ioo 
parts of solution is enough for ordinary purposes, but a good 
proportion is two or two and a half in ioo ; some platers use 
as much as ten in ioo. The following proportions were 
employed by M. Roulz, viz. a solution of one part by weight 
of cyanide of silver and ten parts of cyanide of potassium, in 
ioo parts of water; the mixture being diluted with water to 
the desired strength. 

Making cyanide of silver plating solution by chemical 'means. 
— Take four parts of grain silver, add it, in small portions at 
a time, to a warm mixture of about six and a half parts by 
weight of pure and strong nitric acid, and one part of water, 
contained in a capacious glass or stoneware vessel. Gas will 
be evolved from the surfaces of the pieces of silver, and 
reddish-brown fumes of nitrous anhydride will arise from the 
mixture, and should be conveyed out of the apartment by 
means of a chimney. The action should be maintained 
moderate and unifonn, and, if it should become too strong, a 
little cold distilled water should be added, and the mixture 
kept more cool ; when the whole of the metal is dissolved, 
evaporate the solution nearly to dryness, which will drive off 
any excess of acid that may be present ; the resulting salt, 
nitrate of silver, may then be dissolved in a large quantity 
of distilled water, in the proportion of half a gallon (more or 
less) to each ounce of the silver used. At the same time a 
solution should be made of from two to three parts (accord- 
ing to its quality) of cyanide of potassium in twenty or thirty 
parts of distilled water, which is to be added gradually to the 
solution of nitrate of silver as long as it produces a precipi- 
tate ; if too much be added, it will cause some of the pre- 
cipitate to redissolve and be wasted ; it will also make the 
liquid appear clear and slightly brown where it passes ; in 
such a case the liquid should be stirred, then allowed to settle 
clear, and a small quantity of nitrate of silver dissolved in 



Making Silver Plating Solutions. 157 

distilled water should be added as long as it produces a white 
cloud. By conducting the operation in a glass vessel, add- 
ing the liquid towards the latter period in small quantities 
at a time, and at intervals of a few minutes each, with gentle 
stirring immediately upon each addition, carefully observing 
when it ceases to produce a precipitate, the point of neutral- 
isation may be very accurately arrived at. The liquid must 
now be allowed to remain undisturbed until quite clear, the 
clear portion poured steadily away from the precipitate of 
cyanide of silver, and the precipitate washed five or six times 
in a large quantity of water, by simply adding the water 
briskly to it, allowing it to settle, and then pouring away the 
clear portion. Next dissolve from six to eight parts (accord- 
ing to its quality) of cyanide of potassium in twenty parts of 
distilled water, adding it in portions at a time to the wet 
cyanide of silver, with free stirring, until barely the whole is 
dissolved ; then add about three parts more of cyanide of 
potassium to form free cyanide, and sufficient distilled water 
to reduce the whole to the proportion of about one ounce 
of silver to the gallon : finally, when all the free cyanide is 
dissolved, filter the solution through a piece of unglazed 
calico. On the small scale, distilled water is used in all 
the various parts of the process, except the washing ; but, 
on the large scale, clean rain-water may be used in all the 
operations. 

If either the nitric acid, or the water in which the nitrate 
of silver is dissolved, contains chlorides, a white residue of 
chloride of silver will be left on dissolving the nitrate ; and 
if a small amount of brown matter is left on dissolving the 
cyanide of silver in the cyanide of potassium solution, it 
arises from decomposition of some of the latter salt. The 
insoluble matters and the wash-waters should be reserved 
for the purpose of recovering from them any traces of silver 
they may contain. The numbers given above are based upon 
the assumption that the cyanide of potassium employed is 
of an average quality, and contains about 50 per cent, of the 



1 5 8 The A rt of Electro- Metallurgy. 

actual substance ; in proportion as the percentage is higher, 
so will the quantity required be less. 

The following solution is said to be an excellent one ; 
water iooo parts, pure cyanide of potassium fifty parts, silver, 
for converting into cyanide, twenty-five parts. The silver is 
converted into nitrate. The nitrate is dissolved in distilled 
water, and prussic acid added until it produces no more 
precipitate. The cyanide of silver is filtered and washed, 
and then added to the water and cyanide of potassium. 
This method is only suitable for making small quantities of 
solution, because the ordinary prussic acid is so dilute, 

Some operators have employed the plan of forming 
cyanide of silver by generating hydrocyanic acid gas, by 
heating a mixture of dilute sulphuric acid and coarsely- 
powdered ferro-cyanide of potassium in a glass flask, and 
passing the evolved hydrocyanic acid (prussic acid) vapour 
through a solution of argentic nitrate as long as a precipitate 
is formed, and this yields a slightly purer cyanide of silver 
than that prepared by precipitation, but it is a slow and not 
an economical process, and the prussic acid vapour is highly 
dangerous to inhale. 

The cyanide of silver plating solution may be made by 
other modifications of the chemical method than the one 
described ; for instance, some depositors make the solutions 
by adding oxide, carbonate, or even chloride of silver to a 
solution of cyanide of potassium, as long as it will dissolve, 
and then adding an amount of free cyanide ; by this process 
the depositor is enabled to use caustic potash, carbonate 
of potash, hydrochloric acid, or common salt, instead of 
cyanide of potassium, for precipitating the nitrate of silver ; 
nevertheless it still requires two equivalents of cyanide of 
potassium to be used as before, viz. one to convert the salt 
of silver into cyanide, and the other to dissolve the cyanide 
of silver formed, because, in all such cases, according to the 
researches of Messrs. Glassford & Napier (' Philosophical 
Magazine,' 1844), when any salt of silver is added to a solu- 



Making Silver Plati7ig Solutions. 159 

tion of cyanide of potassium, it is first converted into cyanide 
of silver at the expense of one portion of the cyanide of po- 
tassium, it then combines with the remaining cyanide to 
form double cyanide of silver and potassium, which dissolves 
in the water, therefore by this modification of the chemical 
method no cyanide of potassium is saved, and the carbon- 
ate of potash, hydrochloric acid, &c, are wasted. This 
modification has a still greater disadvantage ; it introduces 
substances into the depositing liquid which are injurious. 
A good depositing solution should dissolve the anode freely, 
hold abundance of metal in solution, and not act chemically 
upon base metals, because it is such metals we generally 
wish to coat ; now, if instead of cyanide of silver we add 
oxide of silver to the cyanide of potassium liquid, it converts 
part of the cyanide into caustic potash ; if we add carbonate 
of silver, it converts it into carbonate of potash ; and if 
chloride of silver, it converts it into chloride of potassium ; 
and each of these substances, especially the last, diminishes 
the action of the liquid upon the dissolving plate, decreases 
its solvent power for cyanide of silver, makes its particles 
less mobile, and causes it to act in some degree upon base 
metals, and thus endangers the adhesion of the deposits 
upon them. Some electro-platers think the presence of 
these salts not injurious, but most consider them highly 
detrimental. One hundred ounces of silver, converted into 
chloride, and dissolved in cyanide of potassium solution, 
produces s ; xty-nine ounces of chloride of potassium as an 
impurity in the liquid ; or if converted into nitrate, and so 
dissolved, produces ninety-three and a half ounces of nitrate 
of potassium as impurity. 

A good plating liquid should contain one equivalent 
(sixty-five parts) of pure cyanide of potassium, and one 
equivalent (134 parts) of cyanide of silver, besides about 20 to 
50 per cent, of free cyanide, and sufficient water to form a 
thin liquid. It is necessary to have free cyanide, because in 
working the solution insoluble cyanide of silver is formed at 



1 60 The A rt of Electro-Metallurgy. 

the anode, and requires free cyanide of potassium to com- 
bine with it and form the soluble double cyanide ; at the 
same time cyanogen and cyanide of potassium are set free 
at the cathode, or receiving surface, by the deposition of the 
silver ; and as it requires some time for those substances to 
mix with the liquid, and reach the dissolving plate, sufficient 
free cyanide must be provided ; the necessity of having 
sufficient water to form a thin liquid arises from the double 
cyanide formed at the dissolving plate being specifically 
heavier than the solution, and thus having a tendency to 
sink to the bottom, whilst the hydrocyanic acid and cyanide 
of potassium, set free at the surface of the articles, being 
specifically lighter, tend to rise to the surface ; at the same 
time each of them mixes more or less with the surrounding 
liquid by capillary attraction or adhesion, and the more 
dilute the liquid is, the more mobile are its particles, and 
the more rapidly does this mixture take place. This 
explains why strong silver solutions require more frequent 
stirring than weak ones to keep them uniform. In some 
manufactories, where they have steam power at command, 
the articles are kept in constant motion by machinery 
swinging them gently to and fro, but in small electro-plating 
establishments the silver solutions are stirred every evening 
instead. 

Many electro-platers use a cyanide solution containing 
about half an ounce of silver to the gallon, and add a very 
large proportion of free cyanide to make it conduct freely \ 
such a solution has the advantage of being comparatively 
inexpensive in its first formation, quick in working, and 
yields metal of an average character ; but it is rather 
difficult to manage in hot weather, and dissolves the anode 
very rapidly, on account of the large proportion of free 
cyanide. In practice, the amount of silver to the gallon 
varies from half an ounce to about four ounces, but ordinary 
solutions contain about one or two ounces to the gallon ; 
the amount of free cyanide of potassium also varies from 



Silver Electro-Plating Solutions. 1 6 1 

about half the weight of the silver dissolved in the liquid, to 
five or ten times this quantity. A very good proportion, is 
about three-fourths of the weight of the dissolved silver, 
but there is no rule generally recognised in the trade upon 
this point ; some manufacturers use a very large, and others 
a very small proportion. 

Mr. Alexander Parkes took out a patent, dated March 
29th, 1 87 1, for improvements in the solid deposition 
of silver. He converts an ounce of silver into oxide, 
by first dissolving it in nitric acid, and then precipitating it 
by caustic potash ; he then dissolves the oxide, together 
with sixteen ounces of cyanide of potassium, in two gallons of 
water, and uses the resulting liquid for depositing solid articles. 

Solid articles of silver are occasionally made, by first 
forming a thin mould in copper by the electrotype process, 
and then depositing silver upon this mould in a cyanide 
solution (containing about eight ounces of silver per gallon), 
until the deposit is sufficiently thick. The article is then 
immersed in a boiling solution of dilute hydrochloric acid, 
or in a hot one of perchloride of iron, until all the copper 
is dissolved. 

Mr. Edmund Tuck took out a patent, June 4, 1842, for 
' improvements in depositing silver upon german-silver.' 
For plating the commoner quality of that alloy, he uses a 
liquid composed of sulphate of silver, dissolved in a solution 
of carbonate of ammonium, and for the best quality, he 
uses cyanide of silver dissolved in a similar liquid. The 
mixtures are formed, by dissolving seventy parts of the 
carbonate in distilled water, then adding 156 parts of sul- 
phate of silver, or 134 of cyanide of silver, and boiling 
the liquid until the silver salt is dissolved. For coating 
common german-silver, he adds half an ounce of sulphate 
of silver, to a solution of 107 grains of bicarbonate of 
ammonium. 

One plater recommends the use of two liquids, the first 
to ' whiten,' and the second to ' finish.' The whitening 

M 



1 62 The A rt of Electro-Metallurgy. 

one is composed of one gallon of distilled water, two 
and a half troy pounds of cyanide of potassium, eight 
ounces of carbonate of soda, and five of cyanide of silver ; 
and the finishing solution, of one gallon of distilled 
water, four and a half troy ounces of cyanide of potassium, 
and one and a half of cyanide of silver; using a series 
of from three to ten Smee's cells with the first solution, and 
one large cell only foi the second, and keeping the anode 
and articles in the second solution, as closely together as 
possible. By these means, the silver may be made to adhere 
firmly to all kinds of brass, bronze, type-metal, &c, with- 
out the use of mercury. 

Copper, brass, and german- silver, are the best substances 
to deposit silver upon ; lead is a very bad metal for the pur- 
pose, because it is so soft. Articles formed of zinc, or iron, 
are usually coated w ith a film of copper, in a cyanide solution, 
before putting them into the plating liquid. Those formed 
of Britannia-metal, tin, or pewter, are not dipped into acid 
before plating, but into a strong and boiling-hot solution of 
pure caustic potash, and are then either ' scratch-brushed ' 
or taken direct from the alkali, without rinsing in water, 
and immersed in a cyanide of silver solution (at about 
190 Fahr.), containing a considerable proportion of free 
cyanide, with a large anode; and an electric current of 
considerable intensity, is passed through the vat for several 
minutes, until the articles receive a thin coating, they are 
then transferred to the ordinary plating solution, to receive 
the full amount of deposit : steel articles, after being cleaned 
in the hot potash, are dipped (without brushing) into a solu- 
tion of one pound of cyanide of potassium in a gallon of 
water; and then coated thinly with silver in a similar manner, 
before plating. Those of lead are first scraped, or otherwise 
made quite clean and bright, by mechanical means, and then 
treated in the same manner as those of Britannia-metal. 
Articles of copper, brass, or german-silver, after being pro- 
perly cleansed, are dipped into the solution of nitrate of 



Electro- Silvering Base Metals. 163 

mercury (see p. 166), or a very dilute one of cyanide of mer- 
cury and potassium (pp. 95 and 323), then rinsed in a vessel 
of water, and immediately suspended in the depositing vat. 
The preparation of articles by immersion in a bath of cyanide 
of mercury was patented by Dr. H. B. Leeson, June 4. 1842, 
and is in use by the electro-platers of Birmingham. If the 
articles are immersed without this precaution, the deposited 
silver does not always adhere firmly. All articles are attached 
to the cathode, immediately after immersion in the plating 
liquid. 

For preparing articles of tin, lead, zinc, Britannia-metal, 
&c, a cold solution is sometimes employed, containing from 
two to three pounds of cyanide of potassium, and only two 
to five pennyweights of silver per gallon ; and the current 
from the usual battery is passed into it by means of a small 
anode. But, for coating steel direct with a preparatory 
film of silver in this solution, a powerful battery is used, so 
as to evolve hydrogen from the steel surface, and the anode 
is composed of a large sheet of platinum together with a 
small sheet of silver. 

For silvering cast-iron, Bottger recommends a bath com- 
posed of fifteen parts of argentic nitrate dissolved in 250 parts 
of water, to which thirty parts of cyanide of potassium have 
been added. After complete solution, pour the mixture 
into 750 parts of water containing fifteen of common salt. 
The cast-iron articles, after being well cleansed, should be 
placed for a few minutes in nitric acid of sp. gr. 1*2, then 
rinsed thoroughly, and placed in the electro-depositing 
liquid. 

Brass, copper, or nickel articles, also those of iron and 
zinc which have been coppered, may after thorough cleansing, 
be silvered, by treatment with a solution of fourteen grammes 
of silver dissolved in twenty-six grammes of nitric acid, to 
which (after the silver is all dissolved) is added a solution 
of 120 grammes of cyanide of potassium in one litre of water, 
and also twenty-eight grammes of finely powdered chalk. 

m 2 



1 64 The A rt of Electro-Metallurgy. 

The original paper gives further directions for producing dif- 
ferent shades of colour on the silvered articles (C. Paul, 
'Journal of Chemical Society/ vol. xi. p. 955). 

To electro-plate over soft solder. — Clean the articles well 
with alkali, then dip them in red nitrous acid, and thoroughly 
rinse away all the traces of acid. Dip the soldered portion 
for a short time, in a very dilute solution of cyanide of mer- 
cury and potassium (see p. 321). Rinse them again, and 
then place them in the plating vat. 

In addition to cyanide mixtures, other solutions have 
been employed for electro-plating by the separate current 
process ; amongst which the most practical ones are those 
containing the sulphite, or the hyposulphite of silver. To 
form the first of these, the patentee (Mr. Woolrich) directs as 
follows : — ' Take of the best pearlash of commerce, twenty- 
eight pounds, and add to it thirty pounds of water, and boil 
them in an iron vessel until the pearlash is dissolved ; the 
solution should then be poured into an earthenware or other 
suitable vessel, and suffered to stand until the liquor becomes 
cold. It should then be filtered, and fourteen pounds of 
distilled water added ; sulphurous acid gas (obtained by 
any of the known processes) should then be passed into 
the filtered liquor until it is saturated, taking care not to add 
the gas in excess. The liquor should be again filtered, and 
the liquid so filtered, is what I term the solvent, or sulphite 
of potash.' 

' To make the silvering liquor, which I use in coating 
with silver the surface of articles formed of metal or metallic 
alloys : I dissolve twelve ounces of crystallised nitrate of 
silver in three pounds of distilled water, in a clean earthen- 
ware vessel, and add to the. solution, by a little at a time, the 
before mentioned solvent, so long as a whitish-coloured de- 
posit is produced ; care being taken not to add more of the 
solvent than is necessary. After the precipitate has subsided, 
I pour off the supernatant liquor, and wash the sediment 
with distilled water. To the precipitate I add as much of 



Silver Plating Solution by the Battery Process. 16 



the before mentioned solvent as will dissolve it, and 
afterwards add about one-sixth part more, so that the 
solvent may be in excess ; I then stir them well together, 
and let them remain about twenty-four hours, and then filter 
the solution, when it will be ready for use. This is what I 
designate silvering liquor ' (' Repertory of Patent Inventions,' 
5th series, 1843, P- 210). This liquid is a ver) good 
one, except that it gradually decomposes and deposits its 
silver, by the influence of light. 

The simplest way of forming the hyposulphite plating 
liquid, is by dissolving chloride of silver in a solution of 
crystals of hyposulphite of sodium. The liquid yields its 
metal easily by means of the electric current, but under the 
influence of light it is decomposed, and its silver falls to the 
bottom in the form of sulphide. 

Mr. Alexander Parkes also took out a patent, October 29, 
1844, for depositing silver by means of a battery and a silver 
anode, from melted chloride or iodide of silver, with or with- 
out the addition of from half to one and a half times its 
weight of iodide of potassium, to increase the bulk of the 
liquid ; and for gilding in a fused mixture of two parts of 
iodide of gold and eight parts of iodide of potassium ; but 
neither process appears to have been much used. 

Mixtures composed of cyanide of silver dissolved in solu- 
tions of ferro-cyanide of potassium, in the proportion of one 
ounce of silver, to three pounds of the cyanide, have also been 
employed for plating, and yield with a feeble current, an ex- 
cellent deposit of soft silver, but the silver anode becomes 
covered with an insoluble white crust, which falls off, and 
the solution soon becomes exhausted of metal. 

Making silver plating liquid by battery process. — The or- 
dinary cyanide of silver plating solution may very conve- 
niently be made by the battery, process, and by some platers 
this plan is preferred to all others. To make by this method, 
a solution containing one ounce of silver per gallon— fust 
ascertain the percentage of actual cyanide in the salt of 



1 66 The A rt of Electro-Metallurgy. 

potassium to be used. If it contains about 50 percent, dis- 
solve about three ounces of it in each gallon (=160 ounces) 
of distilled water ; or if it contains more, add less, and if 
less, add more, in proportion. Suspend a large anode and 
a small cathode of silver, in the liquid ; and pass a strong 
current of electricity, until about one ounce of silver for each 
gallon of liquid has dissolved from the anode, or until with 
a moderate current, and electrodes of average size, a bright 
silver or other suitable cathode, receives a good deposit. As 
this process produces some caustic potash in the liquid, 
some of the strongest hydrocyanic acid may now be added 
to form cyanide, and some more silver then dissolved in 
the mixture by the battery process. 

Condensed oittline of the silver plating process. — (According 
to the French method.) Immerse the articles of copper, 
brass, or german-silver, during a few minutes, in a boiling 
solution of one part of caustic potash in ten parts of water. 
Swill them thoroughly in clean water. Dip them into a 
liquid, composed of ten parts of water, and one of sulphuric 
acid. Rinse them again. Immerse them during a few 
seconds in a mixture of twenty parts of common salt, twenty 
of calcined soot, and tooo of yellow nitric acid of specific 
gravity 1*332, and swill them as quickly as possible in plenty 
of water. Dip them also rapidly in a mixture (prepared 
some time beforehand) of one part of sulphuric acid, sp. gr. 
1*846, forty of common salt, and 1000 of yellow nitric acid, 
of specific gravity 1*332 ; and instantly wash them well in 
clean water. Dip them at once for a few seconds, or until 
they are quite white, in a ' quicking ' solution, composed 
of ten parts of nitrate of binoxide of mercury, and 1000 parts 
of water containing sufficient sulphuric acid to make the 
solution clear; and swill them again in the fresh water. 
Immerse them in the plating liquid, using a weak current, 
and if the deposit looks good, continue the process, but 
if it looks uneven or spotted, take them out, ■ scratch-brush ' 
them, dip them into a hot solution of cyanide of potassium, 



Bright Silver Deposition. 167 

and then in fresh water ; ' quick ' them afresh, rinse them 
again, and then continue the process. When the plating is 
finished, stop the current a few minutes, before removing the 
articles, in order to remove subsalts of silver from the 
deposit, and prevent its turning yellow. Swill them in 
water, then in water slightly acidified by sulphuric acid, 
again finally in water, scratch-brush them if necessary, swill 
them again, dry them in hot sawdust of boxwood, and weigh 
them. 

Bright silver deposition. — The history of the discovery 
of this kind of plating has already been given (see pp. 26, 
27). The brightening effect is produced by attending to the 
following directions. Take one quart of ordinary cyanide 
of silver plating liquid, old liquid by preference, containing 
two pounds of cyanide of potassium per gallon, add to it 
four ounces of strong liquor ammonia, four of bisulphide of 
carbon, and two of ether, and shake it occasionally. After 
it has stood twenty-four hours, add two ounces of the super- 
natant liquid, to 20 gallons of ordinary silver plating solu- 
tion, with gentle stirring, every alternate day. Or add it 
every day, during the morning in summer, and evening in 
winter. But in every case it is highly important, to add 
only the least possible quantity necessary to prod nee the 
effect ; for a greater number of silver plating solutions have 
been spoiled, by addition of an excess of brightening liquid, 
than by all other causes put together. If too much ' bright ' is 
added, the plated articles become of a brown colour, and fre- 
quently spotted. The bisulphide of carbon mixture gradually 
becomes nearly black ; it may stand an indefinite length of 
time, and as often as two ounces of the supernatant liquid is 
taken out, an equal volume of old plating solution strong in 
cyanide, or a strong solution of cyanide alone, should be 
added ; this gradually decreases its blackness, and also pre 
vents its producing a precipitate when added to the solution 
in the vat. 

Messrs. Lyons and W. Milward, the patentees of the pro- 



1 68 The A rt of Electro-Metallurgy, 

cess, give in their patent of March 23, 1847, the following in- 
structions for forming a ' bright solution.' ' Add to the usual 
solution of silver in cyanide of potassium, bisulphide of 
carbon, terchloride or other chloride of carbon, sesqui- 
chloride of sulphur, or hyposulphite of either potash or soda. 
The bisulphide of carbon may be used alone, or dissolved in 
sulphuric ether ; or it may be used in conjunction with any 
of the other substances mentioned above. But the patentees 
prefer using it as follows : — Six ounces of bisulphide of 
carbon are put into a stoppered bottle, and one gallon of the 
usual plating liquid added to it ; the mixture is then shaken 
and set aside for twenty- four hours ; two ounces of the re- 
sulting solution are then added to every twenty gallons of the 
ordinary plating solution in the vat, and the whole stirred 
together ; this proportion must be added every day, on 
account of the loss by evaporation ; but when the mixture 
has been made several days, less than this may be used 
at a time ; (when hydrocarbons are used instead of the 
bisulphide, a much larger quantity must be added.) 
This proportion gives a bright deposit, but by adding a 
larger amount, a dead surface may be obtained very dif- 
ferent to the ordinary dead surface.' This substance is 
generally employed throughout the trade. Other com- 
pounds have also been used, but to a very limited extent ; 
among these are sulphur and collodion. A solution of 
iodine and gutta-percha in chloroform is said to be more per- 
manent in its effect than the bisulphide of carbon. Also one 
and a half ounces each, of the carbonate and acid carbonate 
of potassium, added once in nine or ten days, to a plating 
liquid, containing twelve ounces of cyanide of potassium, 
and three and a half of silver per gallon, is said to produce 
the same effect. But these do not equal the bisulphide. 
(M. Plante silvers brightly, by adding a little sulphide of 
silver to the bath.) The brightening liquid is added to the 
ordinary silver cyanide plating solution, and the proportion 
either of silver or of free cyanide, per gallon, is not a matter 



Vats for containing Silver Solutions. 169 

of much importance. The liquid in a brightening vat is 
always slightly cloudy. 

Articles in the brightening solution become plated more 
slowly than in the ordinary plating liquid. They commence 
to become bright first at their lower parts, and become 
wholly bright in about fifteen minutes. The ' bright ' vat is 
only used to 'finish' articles in, because its only service is 
to impart a superficial appearance. The electric current 
required, is stronger than that for ordinary silver plating. 
Silver deposited from a brightening solution is not however 
pure silver. I have found sulphur in it, by dissolving it in 
pure dilute nitric acid, determining the amount of silver, 
and testing for sulphuric acid, in two separate portions. 
Bright silver is also harder than that deposited from the 
ordinary cyanide solutions, and has very much the appear- 
ance of fused metal. If there are very small holes in the 
surface of the bright articles, dull streaks appear above 
them. Silver deposited in bright vats, blackens quickly on 
removal from the liquid, unless immersed in boiling water 
for a short time. 

Vats for containing silver solutions. — These are of various 
dimensions and proportions, but usually they are about six feet 
long, three feet wide, and nearly three feet deep ; and they 
often contain 200 or 300 gallons of the liquid. They are made 
of different materials ; some are composed of wood only, 
others of two thicknesses of wood with lead between ; but the 
use of wooden vats is nearly discontinued, because they absorb 
a large quantity of the solution, become saturated with it, 
and it soaks through to the outside. A lining of gutta- 
percha cannot be employed, because cyanide of potassium 
acts upon the joints of that substance. They are now made of 
wrought iron, sometimes with a thin layer of wood as a lining 
upon the sides to prevent the anodes touching them, or they 
are lined entirely with cement, but the cement yields up a 
little impurity (probably oxide of iron) to the liquid. 

Each vat has a wooden rim securely fixed to its upper 



170 



The Art of Electro-Metallurgy, 



edge all round it ; upon this rim is fixed a rectangle of brass 
tubing (see annexed sketch, Fig. 23) an inch in diameter, to 
which is soldered a large binding-screw, for connection with 
the positive pole of the battery. Within this rectangle of 
tubing is also similarly fixed, but insulated from the first one, 
a smaller rectangle of brass-tubing, about half an inch in dia- 
meter, with a screw for connection with the negative pole. 
Cross tubes of brass, about half an inch in diameter and as 



Fig. 23. 




long as the vat is wide, are laid in clean metallic contact 
upon the larger rectangle, and these cross tubes support, and 
are metallically connected with the large and flat sheet silver 
anodes, by means of frames of iron, which extend downwards 
into the liquid. Similar, but shorter brass tubes, are laid 
across the vat, with their ends upon the inner rectangle, and 
these support, by means of wires, the articles to be coated. 
All the points of contact of the cross tubes with the rect- 
angles, the supporting frames and wires with the cross tubes, 



Suspending Articles for Plating. 



171 



and the other connections, are frequently examined, and kept 
scrupulously clean, by means of rubbing with emery cloth. 

The wires for supporting the articles are usually formed 
of copper about the thickness of bell-wire, and are protected 
(excepting their ends and those parts which are not im- 
mersed in the liquid) from receiving a useless deposit of 
silver, by enclosing them in short tubes of glass, gutta- 
percha, or pure india-rubber ; and are bent at their lower 
ends into a sort of a loop, when required to support forks or 
spoons, so that those articles may be readily slipped into the 
loops and supported. (See Figs. 24, 25.) 



Fig. 24. 



Fig. 25. 





In vats where the articles are kept in continual motion, 
the cross rods supporting them are fixed to an iron frame, 
with four small wheels (about three inches diameter), which 
move backwards and forwards to an extent of three or four 
inches upon inclined rails fixed upon the edges of the vat, 
and impart to the articles a combined vertical and horizontal 
swinging motion, or they are suspended from a swinging- 
frame. (See Fig. 26, p. 174.) 

Quality of the deposited silver. — The quality of the de- 
posited silver, like that of all other metals, depends chiefly 
upon two circumstances, viz. the strength of the current in 



1 7 2 The A rt of Electro-Metallurgy. 

relation to the magnitude of surface of the article to be 
coated, and the composition and temperature of the plating 
solution. If the articles become grey or black in the solu- 
tion, and evolve much gas, the current is too strong, and 
either the number of battery cells, or the depth of immer- 
sion of the battery-plates, must be diminished. If the de- 
posit is good, but not sufficiently rapid, it is best increased 
by greater surface of immersion of the battery-plates. 

Management of cyanide plating solutions. — Cyanide of 
silver plating liquid is more easily managed than cyanide 
gilding solution, and less easily than the ordinary sulphate 
solution employed in depositing copper. 

There are various circumstances which must be attended 
to, in order to keep a cyanide plating liquid in proper 
condition for yielding a good and suitable deposit of silver, 
and to restore it to that state when it has changed from 
it. A new silver solution does not usually work as well as 
an old one, provided the latter is not too old. Solutions which 
are two or three years old work very well, but those which 
have been in use ten or twelve years, often work badly, 
because they generally by that time become too impure. 

Cyanide plating solutions are liable to change from 
several circumstances. They become dirty with sus- 
pended solid particles. They become more concen- 
trated, and of greater density, by evaporation of water, addi- 
tion of cyanide of potassium, increased proportion of silver, 
&c. They either increase or decrease in their proportions 
of silver or cyanide by various causes ; if that of cyanide 
of potassium to silver is large, or if the anode is large 
in relation to the receiving surfaces, the proportion of 
silver increases, and of free cyanide decreases ; if the anode 
is relatively small, reverse effects take place. They acquire 
various metals besides silver, in solution, by corroding 
articles immersed in them to be plated, and also by dissolv- 
ing impurities from the anode. They gradually decompose, 
become brown, and evolve ammonia by exposure to light, 



Management of Cyanide Plating Solutions. 173 

especially if they contain much free cyanide. They become 
spoiled by addition of too much brightening liquid ;and so on. 

If the solution contains suspended solid particles, or 
sediment which is liable to rise by the motion of the liquid, 
the impurities settle upon the receiving surfaces, and produce 
a rough or uneven deposit, with vertical streaks ascending 
from them, especially if the articles are still, the liquid 
dense, and the deposition rapid. Solutions should therefore 
be filtered when necessary. 

If the liquid is too dense, the articles still, and deposi- 
tion is rapidly occurring, the goods are liable to become 
covered with vertical streaks, and to receive a much thicker 
deposit upon their lower parts than upon their upper 
ones. If the ■ density is due to foreign salts, crystals 
of those salts are liable to form upon the articles in cold 
weather, and spoil the deposit. The specific gravity of a 
cyanide plating solution, may vary from 1*036 to rn6 
without detriment to the quality of the deposited metal, 
provided the greater density is not due to sparingly soluble 
substances ; if the density is greater than this, water may be 
added. The specific gravity of an old plating solution, 
analysed by me, was 1-1821 at 65 Fahr. ; it contained 16960 
grains of solid matter (including 499 grains of silver), per 
gallon. If the solution contains too little water, but has 
the silver and cyanide in their proper relative proportions, it 
conducts freely, and gives a good and quick deposit; but 
is more difficult to manage than a weaker liquid, especially 
in hot weather, because, from the less mobility of its particles, 
it is more apt to settle into strata of different specific 
gravities ; its lower layers become nearly saturated with 
silver, and destitute of free cyanide, and its upper ones 
become exhausted of silver, and strongly charged with free 
cyanide. In consequence of this, the upper parts of the 
anode dissolve rapidly, whilst the upper parts of the articles 
receive very little deposit, and. the lower parts of them are 
coated too rapidly, and neither receive a deposit of the best 



174 



The A rt of Electro-Metallurgy. 



quality. All these evil effects may be diminished in such a 
solution, by stirring it well every night, after having finished 
plating, or they may be entirely prevented by diluting the 
liquid to a proper degree, and stirring it every evening. If 
the solution is too weak (i.e. contains too much water), it 
conducts sparingly, deposits slowly, and the deposit has a 
' dead ' white appearance. This may be easily remedied by 
adding cyanide of silver and cyanide of potassium to it in 
proper proportions, and working it uniformly during a few 

Fig. 26. 




days. The evil effects of improper degree of density of 
the solution upon the quality of the deposited metal, may 
be diminished, by keeping the articles in a state of gentle 
motion, by means of an apparatus (such as is shewn in Fig. 
26) ; driven by power from a steam-engine. 

If the anode is dirty, it indicates a deficiency of cyanide 
of potassium: this may be remedied by adding that sub- 
stance ; but if the liquid contains much carbonate of potas- 



Management of Cyanide Plating Solutions. 175 

sium, as it usually does, either as an impurity of the cyanide 
employed, or by decomposition of the cyanide by light, as 
in a brown old solution, it may be remedied by addition of 
hydrocyanic acid, which will convert the carbonate into 
cyanide. The necessity of adding a little fresh cyanide is 
indicated, when the dissolving plate begins to change from 
its ordinary pure white appearance to a dull yellowish grey 
colour. It is best added in the evening after plating, about 
half an hour before stirring the solution. 

If the anode appears grey during the passage of the 
current, and white whilst the current is stopped ; and if in 
addition to this, the deposit of metal is good, the solution is 
usually in proper condition. But if the anode is dark coloured 
or black whilst the current is passing, there is probably either 
too small a proportion of cyanide of potassium, or too large a 
one of silver; but if it is white, the reverse. If the cold 
solution coats bright copper rapidly with silver by simple 
immersion only, it probably contains too much free cyanide 
of potassium ; a bath should not produce this effect without 
the aid of a separate current. A solution containing much 
free cyanide, causes the anodes to corrode in holes, and fall to 
pieces, especially if the anodes touch the iron vat ; it also 
becomes rapidly richer in silver, and thus cures its own defect. 
The proportion of free cyanide may vary greatly without 
much injury to the solution, or to the quality of the deposited 
metal. One part of good cyanide of potassium is sufficient 
to dissolve one part of silver when converted into cyanide ; 
but unless there is, in addition to the quantity actually re- 
quisite to retain the silver in solution, a considerable excess 
of free cyanide of potassium, the conduction is defective, 
and the deposit granular and irregular. 

To quickly ascertain if the plating liquid contains the 
proper proportion of silver to cyanide : — Put twenty-live 
parts by weight of the solution into a tall glass, and add to it, 
at first freely, but towards the last, drop by drop, with con- 
stant stirring, a solution of one part of crystallised argentic- 



1 7 6 The A rt of Electro-Metallurgy. 

nitrate in ten parts of water. If the precipitate formed dissolves 
rapidly, with but little need of stirring, there is too little silver 
or too much cyanide. If it does not all dissolve, even after 
much stirring, there is too little cyanide, or too much silver, 
but if it wholly dissolves (the latter portions quite slowly), 
the proportion of silver to cyanide is about correct. 

If a solution contains a great excess of free cyanide, and 
is also deficient in water, it becomes in hot weather very 
difficult to manage, and emits strongly the odours of 
ammonia and hydrocyanic acid. In such a solution, if 
from any cause the battery current becomes suddenly weak 
towards the evening, the silver deposited upon the articles 
will be re-dissolved, in consequence of the liquid about 
the anodes, having by the day's work, become saturated 
with silver, and that about the articles, become full of free 
cyanide ; the two electrodes (i.e. the dissolving plates and the 
articles) form a kind of voltaic battery, (of one metal in two 
liquids, see p. 69), which develops a current of electricity in 
an opposite direction to the original one, and thus re-dissolves 
the deposited silver. (See 'Polarization of electrodes,' p. 54.) 

On some rare occasions, gas rises freely from the silver 
dissolving plate alone, and when this occurs, if the plate and 
articles are disconnected from the battery, and the ends of 
the wires brought into contact, and then suddenly separated, 
a minute spark (visible in the dark), is seen, produced by a 
current opposite in direction to that of the battery current, 
and probably produced by some polar conditions of the 
dissolving and receiving surfaces. This will even occur 
when the articles are kept in constant motion, and even 
after the dissolving plate has been taken out of the liquid, 
and re-immersed after the lapse of half an hour. On such 
occasions there is a tendency to a gritty deposit, and the 
solution is said to be out of order. (See p. 54.) 

Peculiar phenomena often occur in the electro-deposi- 
tion of silver, not only upon different metals, but also upon 
the same metals in different forms, or under other conditions 



Management of Cyanide Plating Liquids. 177 

of surface. For instance, if two perfectly similar pieces of 
thin sheet brass are taken (except, that one is perforated all 
over with small holes), and both be simultaneously immersed 
in the same solution to be silvered, and with the same 
battery power applied to each, the latter, although its amount 
of surface is reduced by the perforations, is said to become 
coated with silver much more slowly than the former. If a 
wire gauze cylinder of a Davy lamp, be suspended side by 
side with a piece of thin tubing of the same metal, and of the 
same dimensions, the latter will become coated much more 
rapidly than the former. If two pieces of the same metal, 
iron for instance, be immersed to be silvered in the ordinary 
cyanide solution, or to be coppered in the hot cyanide 
of copper and potassium liquid, each containing exactly the 
same amount of surface to be coated, but one being in the 
form of a thin sheet, and the other in that of a thick plate, 
or solid block of metal, the former will become coated 
much more rapidly than the latter. The edges and points 
of articles, whilst being plated, exhibit a greater tendency to 
a crystalline deposit than the flat parts, and this tendency 
is sometimes manifested in depositing silver upon table 
knives and forks. It is the knowledge of these, and many 
other peculiarities, of different metals and articles met with 
in practical working, and of the means of overcoming their at- 
tendant difficulties, which constitutes one of the chief differ- 
ences between the practical operator, and the theoretical man. 
Electro-deposited silver is sometimes of a yellow colour, 
and occasionally pinkish ; these colours are due to impurities. 
The yellow appearance, which silver deposited from a cyanide 
solution, sometimes assumes after having been out of the 
liquid, is said to be due to subcyanide of silver in the deposit, 
and the pinkish tint is probably due to copper. Liquid 
ammonia, added to cyanide of silver plating solution not 
containing much free cyanide of potassium, frequently im- 
proves the colour of the deposit, and the condition of the 
liquid. 

N 



i;8 The Art of Electro-Metallurgy. 

A bright solution is much more difficult to manage 
than the ordinary silver liquid ; if it is not worked constantly, 
and in an uniform manner, it will lose its power of yielding 
bright metal. If any of the articles which are being 
plated in it are disturbed, or removed from the liquid and re- 
placed, those will not now receive a bright deposit, and the 
disturbance of the liquid by their removal, will oftentimes 
cause all the neighbouring articles to lose their brightness. 
If too much ' brightening liquid ' is added, the solution will 
be considerably injured ; many silver solutions have been 
irretrievably damaged in this way. A bright solution 
requires a battery current of large quantity to work it, and 
the dissolving plates in it are generally of a darker colour 
than those in the ordinary silvering liquid. 

Rapidity of silver deposition. — The rapidity with which 
metal of good quality can be deposited, depends largely 
upon the composition of the solution. To work rapidly, 
the solution should contain a rather large proportion of 
free cyanide of potassium, otherwise, the anode becomes 
covered with an insoluble film, before free cyanide from the 
articles can diffuse to it, and this film impedes the current. 
In a good silver solution, a dozen of ordinary table spoons 
or forks will acquire iooo to 1500 grains of silver in twelve 
hours, but there are solutions used in Birmingham, in which 
it is said as much as one ounce of silver can be deposited 
upon a small table spoon in half a day. 

Thickness of deposited silver. — Electro-plated articles vary 
greatly in quality, because any degree of thinness of silver 
may be put upon them. Great quantities of Britannia-metal 
articles are coated with only a few pennyweights of silver 
per square foot. ' The thickness of electro-deposited silver 
is in many cases from ^V 11 ^ to ^foth, or even wVoth °f a 
millimetre, or 1*24 grains upon a square metre of surface.' 
One ounce of silver per square foot of surface, is equal to a 
coating of about the thickness of thin writing-paper, and 
is considered an excellent coating. The prominent parts of 



Thickness of Deposited Silver. 1 79 

a plated article usually receive the thickest coating, because 
electricity enters and leaves the projecting parts of bodies 
more readily than their hollow parts, and in deposition the 
prominences of the anode receive the most perfect supply of 
free cyanide, and those of the cathode receive chiefly the 
supply of saturated solution. ' M. M. Christofle, during the 
year 1865, deposited 33,600 kilogrammes of silver, upon 
5,600,000 objects j and covered a surface of 112,000 square 
metres, with three grammes of silver upon each square centi- 
metre.' 

'In France, electro-plating is regulated by law, every 
manufacturer being required to weigh each article when 
ready for plating, in the presence of a comptroller appointed 
by the Government, and to report the same article for 
weighing again when the plating has been done. In this 
way, the comptroller knows to the fraction of a grain, the 
amount of precious metal that has been added, and puts 
his mark upon the wares accordingly, so that every pur- 
chaser, may know at a glance, what he is buying. As to the 
amount of silver consumed in ordinary plating — an ounce 
and a half of silver will give to a surface a foot square, a coat- 
ing as thick as common writing-paper, and, since silver is 
worth five shillings per ounce, the value of the silver covering 
a foot square, would be about seven-and-sixpence. At this 
rate, a tea-pot or coffee-pot is well plated, at a cost in silver, 
of not more than seven or eight shillings. The other expenses, 
including labour, would hardly be more than half that amount. 

' The popular notion is, that genuine electro-gilding 
must necessarily add a good deal to the cost of the article 
coated. This is erroneous. A silver thimble may be 
handsomely coated, so as to have the appearance of being 
all gold, for threepence, a pencil case for tenpence, and a 
watch case for four shillings. An estimate of the relative 
value of electro-gilding as compared with silver plating, 
considering the cost of material alone, is about five to one. 
The quantity of silver used in plating the wares sent in such 

n 2 



1 80 The A rt of Electro-Metallurgy. 

large quantities to the colonies, is about an ounce to the 
square mile ; one hard cleaning exposes the base metal, and 
your bargain from auction or cheap store, may be thrown 
on the dust heap' ('Technologist'). In Birmingham iron 
snuffers are sometimes ' silvered ' wholesale, at as low a 
price as fourpence per pair ; and hooks and eyes, at one 
penny per pound. 

In England also, the articles are weighed both before and 
after plating ; some French electro-platers use a ' plating 
balance,' the articles being suspended from one end of the 
beam, and a scale pan containing weights from the other, 
by means of which, when the articles have received any 
desired amount of deposit (determined beforehand), the 
circuit is automatically broken, and the deposition stopped. 

The average cost of depositing silver has been estimated 
at twopence per ounce, but this would probably only include 
fhe cost of the battery power, and not of the numerous other 
incidental expenses. A very large amount of plating is done, 
at a cost of about eight shillings per ounce of deposited silver, 
by professed electro-platers (* electro-platers to the trade '), 
whose sole occupation is electro-deposition, for others, who 
are called ' electro-platers. Many manufacturers of spoons, 
forks, tea-pots, coffee-pots and other articles, have at different 
times commenced to plate for themselves, but have found, 
that the coated articles were so often required to be stripped 
and re-plated, and that the difficulties and incidental ex- 
penses were so great, that they have abandoned the actual 
performance of the process, and send the articles to the 
regular ' electro-platers to the trade ' to be done. 

Ornamenting silver articles. Dead silver ; l Oxidised 
silver.'' — Frequently, for the purposes of ornamentation, and 
of producing a pleasing effect, the surface of deposited 
silver is treated in various ways. To obtain what is termed 
a 'dead' appearance, like frosted silver, deposit a mere 
trace of copper upon it in a sulphate of copper solution, 
and then a very thin layer of silver upon that. ' Oxidised ' 



Ornamenting Silver-Plated A r tides. 1 8 1 

silver, is not silver coated with oxide, but with a film of 
platinum, or of sulphide of silver ; the former is produced, 
by applying a hot solution of perchloride of platinum, and 
allowing it to dry ; the colour varies from a light steel-gre) 
to nearly black. The hotter the solution, and the greater 
proportion of platinum in it, the deeper black does it pro- 
duce. The colour arises from finely divided black metallic 
platinum, deposited by simple immersion process ; and the 
silver is slightly corroded by the action, forming chloride 
of silver, which may be dissolved by means of diluted 
aqueous ammonia. A bluish black colour is produced by 
means of a freshly made, and hot solution, of sulphide of 
potassium (' liver of sulphur '). ' Nielled silvering ' is a 
process of sulphurising engraved parts of silver surfaces, 
and consists in inlaying the surface with sulphide of silver 
which has been prepared beforehand, and causing it to 
adhere firmly to the metal, by heating the article in a muffle 
until the sulphide melts. This, however, is a separate art. 
closely allied to enamelling. 

To produce a beautiful pink colour upon silver, dip the 
clean article for a few seconds in a hot and strong solution 
of cupric chloride, swill it in water, and then dry it, or dip it 
in spirit of wine, and ignite the spirit. (W. H. Fearn.) 

A blackish colour is sometimes produced, by making a 
thin magma of plumbago and spirit of turpentine, and 
rubbing it upon the surface. After drying, the black is 
rubbed off from the prominent parts of the surface by means 
of a rag wetted with alcohol ; the process is called ' old or 
antique silvering.' To produce a brownish-black colour upon 
silver articles, a solution, composed of equal weights of salam- 
moniac and sulphate of copper dissolved in vinegar, is applied. 

Articles of silver are also ornamented, by depositing 
gold upon portions of their surfaces ; and those of gold are 
ornamented, by depositing gold of different tints of colour 
(sometimes as many as five or six) upon their different 
parts; this is effected by covering the parts which are not 



1 82 The A rt of Electro-Metallurgy. 

to receive the coating, with a varnish which will resist the 
solvent power of the hot alkaline gilding liquid. The com- 
position of such a varnish is as follows : — 

Translucent resin . . . . . .10 parts 

Yellow beeswax 6 ,, 

Extra fine red sealing-wax . . . 4 ,, 
The finest polishing rouge (i. e. impalpable per- 
oxide of iron) -3 5? 

Best quick drying copal varnish, with some peroxide of 
iron, or ultramarine, mixed with it, is used for ' stopping off/ 
in hot cyanide solutions, or mixed with chromate of lead, if 
for use in cold liquids. It dries in about three or four hours. 

Cleaning silver. — A yellow colour upon silver which has 
been electro-deposited, is said to be due to the action of the 
air upon a basic or subcyanide of silver in the pores of 
the metal, and may be removed by immersing the article 
either in a solution of cyanide of potassium, or in ordinary 
plating solution containing free cyanide. A weak solution 
of cyanide of potassium is also a good substance to clean 
discoloured silver, but it dissolves a little silver, and is also 
a very dangerous liquid to be entrusted to ignorant persons, 
being exceedingly poisonous. 

The East Indian jewellers clean silver, by briskly rubbing 
it with slices of a juicy lemon, and then covering the article 
with the slices in a pan for a few hours. They then swill 
them two or three times in water ; stir them in nearly boiling 
soap-suds, brush, rinse, and finally dry them on a metal 
plate over hot water. Green tamarind stems are more power- 
fully detergent than lemons, and are employed to remove 
oxide and fire-marks from gold and silver (' Telegraphic 
Journal,' vol. xi. p. 178). Silver may be cleaned in water in 
which potatoes have been boiled, and a superior polish is 
thus imparted to them (Eisner, ' Chemical Society's Journal,' 
vol. xi. 1072). A good polishing paste for silver, is composed 
of washed whiting, precipitated carbonate of magnesia, and 
precipitated peroxide of iron. 



Stripping Plated A r tides. 1 8 3 

' Stripping ' aiiicles. — Sometimes, articles composed of 
copper, brass, or german-silver, which have been plated 
with a portion of silver, require to have the coating entirely 
removed, and a new deposit put upon them, because 
the first was defective. Occasionally also, the depositor has 
sent to him. to be re-plated, old articles of silvered copper, 
(' Sheffield plate,') the coating upon which has partly worn 
away; these require to have the remaining portions of 
silver removed, in order to obtain a uniform surface 
to deposit upon. The removal of the silver is termed 
' stripping/ To effect this, add a very little nitrate of soda 
(' Chili saltpetre,') to a quantity of strong and hot oil of 
vitriol, and immerse the articles in the mixture, until all the 
silver is dissolved. If the action becomes slow, apply more 
heat, and add more saltpetre at the moment of using. The 
copper will not be much acted upon, if the articles are not 
allowed to remain in too long. A number of such articles 
are generally ' stripped ' together, and are afterwards washed,, 
and prepared in the usual manner for receiving a deposit; or 
the silver may be removed, but more slowly, without the aid 
of heat, by suspending the articles for a greater or less length 
of time, according to the thickness of the coating, in a bulky 
mixture of ten measures of strong sulphuric acid, and one 
measure of concentrated nitric acid, contained in a large 
stoneware vessel. The liquid must not be diluted, but be 
kept as free from water as possible, by not immersing wet 
articles in it, and by keeping it covered from the air ; other- 
wise it will attack the copper, brass, bronze, or german- 
silver base of the articles. As the liquid becomes weaker, 
very small portions of strong nitric acid are added to it. Its 
action is less rapid than that of the hot mixture already de- 
scribed. In stripping an article for re-plating, the whole of 
the silver should be taken off, otherwise the deposit sub- 
sequently put upon it, is apt to shew lines, where silvered 
and unsilvered portions meet. Some depositers re-plate 
defectively coated articles without stripping them ; they 



1 84 The A rt of Electro-Metallurgy. 

merely well ' scratch-brush/ ' buff,' and ' quick ' them re- 
peatedly, and then put on the second coating ; but this is a 
less satisfactory method. 

If the base of the article is composed of iron, steel, zinc, 
or lead, the above mode of stripping by acids is not applic- 
able, and the coating is best removed, by making the articles 
the anode, in an ordinary cyanide of silver plating solution, 
until the silver is dissolved. 

Sometimes it is necessary to perform the converse opera- 
tion, viz. to strip copper from the surface of silver, as when 
a thin copper mould has to be removed from a solid deposit 
of silver formed upon it by electro-plating process. To effect 
this, boil the article in dilute hydrochloric acid, or immerse 
it in a hot solution of perchloride of iron. This latter liquid 
maybe made by digesting peroxide of iron (crocus, or jewel- 
ler's rouge) in warm hydrochloric acid, as long as it will 
dissolve ; the solution will remove tin, lead, or copper, from 
either gold or silver, without affecting those metals. A 
solution of chloride of zinc has been used for the same pur- 
pose. Copper may also be completely removed from silver 
or gold, by making it the anode in a sulphate of copper solu- 
tion, until all the copper is dissolved ; the silver will remain 
unaffected if the current employed is feeble, and has not 
a greater intensity than one or two pairs. 

Sometimes articles of silver which are gilded, require to 
have the gold removed from them ; this is effected by heat- 
ing them to redness, and throwing them into dilute sulphuric 
acid; the gold scales off in spangles, and falls to the bottom. 
The process is repeated until all the gold is removed. With 
articles which are hollow, it is better to make them the anode 
in a solution of one part of cyanide of potassium and ten 
parts of water, with a cathode of platinum. 

Analysis of cyanide of silver plating solutions. — The only 
points usually required to be known respecting the compo- 
sition of a silver plating liquid, are the proportions of free 
cyanide of potassium, and of metallic silver. 



Analysis of Plating Solutions. 1S5 

The common method of ascertaining the percentage of 
free cyanide, is that of Glassford and Napier, and may be 
carried out as follows : — Dissolve a known weight, say fifty 
grains of crystallised nitrate of silver, in distilled water, and 
dilute it to a known weight or bulk. Take a known measure 
of the plating liquid, say one ounce, if it is not extremely 
strong in free cyanide. Add the solution of nitrate to the 
plating liquid, just as long as the precipitate formed dissolves 
completely on stirring, and ascertain how much of the silver 
salt has been consumed. Every 170 parts of nitrate, equal 
130*2 parts of free cyanide. 

The silver of an old cyanide plating solution, cannot be 
satisfactorily converted into pure chloride, by adding an ex- 
cess of hydrochloric acid, and boiling the mixture ; the pre- 
cipitate so obtained is of varied colours, and contains foreign 
substances. To ascertain the amount of silver, evaporate a 
known volume of the solution to dryness, fuse the residue at 
a red heat in a porcelain crucible, cool it, and dissolve the 
saline residue in water (testing the water for silver by means 
of hydrochloric acid), taking care to collect any chloride 
of silver present. Dissolve the metallic residue in warm 
dilute nitric acid ; and estimate the amount of silver in the 
solution, by ordinary volumetric or gravimetric methods. 
The silver may also be estimated as follows, by a method I 
have employed. Take 700 grains by measure of the solu- 
tion ; evaporate it to dryness ; add sixty grains of sulphate, 
and fifteen of nitrate of ammonium, both in powder, mix, and 
dry thoroughly. Transfer the mixture to a capacious porce- 
lain crucible, and heat very gradually to fusion at a low red 
heat. Dissolve the cooled residue in hot dilute nitric acid, 
taking care to collect any undissolved chloride of silver. 
Precipitate the dissolved silver by hydrochloric acid, filter, 
wash, ignite, and weigh the pure argentic chloride, every 
143-5 parts of which equal 108 parts of silver. In this pro- 
cess, all the cyanogen of the solution, is expelled by the 
fusion with the sulphate and nitrate of ammonium, and the 



1 86 The A rt of Electro-Metallurgy. 

base metals and alkalies are converted into soluble sulphates. 
Frequently the fused saline mass is quite green with copper 
and other metals. A sample of plating solution, analysed by 
this method, gave 147 "54 grains of metallic silver per gallon, 
and much copper ; another yielded 499*2 grains, and a 
great quantity of chlorides ; a third 1,720 grains, and 
much copper, iron, and chlorides ; seven others gave 
from 348*1 to 979*9 grains ; six, from 1,701 to 2,195 
grains; and eight yielded from 519 to 865 grains per 
gallon. 

According to G. C. Wittstein, cyanide of silver plating 
solution may be completely analysed as follows : — 1. Mix 
twenty cubic centimetres of the liquid with fourteen cc. of 
acetic acid of 20 per cent. ; evaporate ; extract the residue 
with absolute alcohol ; evaporate the alcoholic solution ; heat 
the residue with hydrochloric acid ; dry, and weigh as chloride 
of potassium (KC1). This gives the total amount of potas- 
sium (K) as free cyanide, as potassic silver cyanide, car- 
bonate, and cyanate. 

2. Take a second twenty cc. of the solution, add sulphide 
of ammonium — (NH 4 ) 2 S — in slight excess, find amount of ar- 
gentic sulphide, and calculate from it the amount of potassium 
in the double cyanide (KCy AgCy). 

3. Precipitate a known portion of the plating liquid 
with calcic chloride, and weigh the carbonate of calcium 
(Ca CO3) ; this gives by calculation the amount of potassic 
carbonate (K2CO3). 

4. As the impure cyanide contains for every seven equi- 
valents of cyanide of potassium, three equivalents of cyanate 
(7 KCy + 3 CyKO), calculate from this and the other data, 
the amount of potassic cyanate. 

And, 5. Deducting from the entire amount of potassic 
chloride obtained in No. 1, the quantity of the same salt 
equivalent to the amount of double cyanide (KCyAgCy), 
the potassic carbonate and potassic cyanate ; the remainder, 
is the amount of potassic chloride, equivalent to the quantity 



Recovering Gold and Silver from Old Solutions. 187 

of free cyanide of potassium in the solution (' Journal of the 
Chemical Society/ vol. xii. p. 10 12). 

Napier (commenting on Wittstein's process) recommends 
a simpler one as follows : — To find the amount of silver, eva- 
porate one ounce of the solution to dryness, and fuse the dry 
residue in a small crucible. Dissolve the saline mass, ob- 
tain the little button of silver, and weigh it; or, precipitate one 
ounce of the solution, by hydrochloric acid in excess ; wash, 
dry, and weigh the product : three-fourths of the weight of 
which is silver. To one ounce of the liquid, add a solution 
of nitrate of silver as long as a cloud is produced ; wash the 
precipitate with water by decantation ; add to it an excess 
of a mixture of equal volumes of nitric acid and water, which, 
by digestion, dissolves all the silver salt not cyanide. Decant 
the liquid, add a little hydrochloric acid to it, wash, dry, and 
weigh any precipitated chloride of silver. One-half of the 
weight of this precipitate, approaches closely to the amount 
of cyanate or carbonate of potassium, the difference in their 
equivalents not being great. If there was any chloride in the 
original plating solution, the chloride of silver corresponding 
to it, will remain in the portion of precipitate insoluble in the 
dilute nitric acid. 

Recovering silver and gold from residuary liquids, &*c} — 
Many silver plating solutions are spoiled by unsuccessful 
attempts to improve them ; by the accidental introduction of 
impurities ; by adding excess of cyanide of potassium; by having 
been improperly made; and especially by addition of too much 
' brightening liquid ; ' and we wish to recover their metal. 
There are two general modes of recovering silver from worn- 
out or spoiled solutions, or waste residuary liquids : one, by 
precipitating the silver as chloride by addition of sufficient 
hydrochloric acid, washing and drying the chloride of silver 
precipitate, and fusing it with carbonate of potassium con- 
taining a little saltpetre to oxidise the baser metals ; and the 
other, by evaporating the solution to dryness, and fusing 
1 See also p. 145. 



1 8 3 The A rt of Electro-Metallurgy. 

the product without the addition of any oxidising substance, 
which would be very dangerous if cyanide of potassium is 
present. In both cases the silver and gold are set free. 

To recover silver from ' stripping ; solution in the form 
of cyanide, dilute the supernatant liquid with water, dissolve 
the precipitated yellow powder, or crystals of sulphate of 
silver, by addition of nitric acid to the water. Pour off ! 
the clear liquid, and add cyanide of potassium to it as long 
as a precipitate of cyanide of silver takes place, or until effer- 
vescence of hydrocyanic acid occurs by decomposition of 
the excess of cyanide of potassium by the free nitric and 
sulphuric acid present. Collect, wash, and dry the precipi- 
tated cyanide of silver ; and, after testing the liquid portion 
with hydrochloric acid to see if it contains any traces of silver, 
throw it away. Another plan is to add a solution of wash- 
ing-soda to the ' stripping-liquid ' until the latter is alkaline 
to red litmus paper (i.e. turns the paper blue), then acidify 
the mixture by addition of hydrochloric acid. After sub- 
sidence, throw away the clear liquid, dry the sediment, and 
fuse it with a mixture of the dried carbonates of potassium 
and sodium containing a little saltpetre. The nearly pure 
silver and gold remains. 

As the recovery of silver and gold from silvering and 
gilding solutions, is an important matter in practical electro- 
metallurgy, I extract the following valuable remarks from a 
paper by Eisner : ' I have undertaken a series of researches 
upon this object, and hasten to communicate the results 
to the public ; but, before proceeding to the communication, 
I think it necessary to mention the results of the experiments, 
upon which are based the methods given further on, for 
extracting both the silver and the gold of old cyanide of 
potassium liquids. 

' i. If we add hydrochloric acid to a solution of silver in 
cyanide of potassium until the liquid exhibits an acid re- 
action, we obtain a white precipitate of chloride of silver, 
which, when submitted to heat, melts into a yellow mass. 



Recovering Gold and Silver from Old Solutions. 189 

If this was cyanide of silver, the application of a red heat 
would have left a regulus of silver. The addition of the hydro- 
chloric acid, precipitates all the silver present in the liquid in 
the form of chloride of silver. 

' 2. If we evaporate a solution of silver in cyanide of po- 
tassium to dryness, and heat the residue to redness, until the 
mass is in a state of quiet fusion, and has assumed a brown 
colour, there remains, when we wash the mass with water, 
metallic and porous silver. The wash waters, when filtered, 
still contain a little silver in solution ; because, if hydro- 
chloric acid is added to them, it produces a precipitate of 
chloride of silver. In evaporating and calcining a solution 
of gold in cyanide of potassium, the result is similar, i.e. we 
obtain metallic gold. The wash waters, acidulated with 
hydrochloric acid, give, when treated with sulphuretted 
hydrogen, a brown precipitate of sulphide of gold ; and, 
with the salt of tin, a violet precipitate (purple of Cassius), — a 
proof that these liquids still contain a little gold in solution. 

' 3. If we pour upon finely-divided silver — for instance, 
silver leaf, or silver precipitated in the porous state by 
zinc, from a solution of silver — a concentrated solution of 
cyanide of potassium, at the ordinary temperature, and shake 
it frequently, the liquid, at the end of a certain time, exhibits 
silver in solution, and by adding hydrochloric acid to it, we 
produce an abundant precipitate of chloride of silver. This 
experiment explains why, in the wash waters of the various 
combinations of gold or silver with cyanide of potassium, we 
can still demonstrate the presence of gold and of silver after 
the most minute separation. 

' 4. When hydrochloric acid, or ordinary sulphuric acid, 
is added to a solution of cyanide of copper and cyanide of 
potassium, until the liquid exhibits an acid reaction, the 
result is a reddish-white precipitate, which is a cyanide of 
copper in the anhydrous state. If the precipitate be well 
washed, and boiled in potash lye, oxide of copper is sepa- 
rated, of a beautiful red colour ; and if to the filtered alka- 



1 90 The A rt of Electro-Metallurgy. 

line liquid we add a solution of green copperas, a dirty-blue 
precipitate is obtained. A solution of carbonate of sodium 
furnishes the same results, and yields with the copperas, the 
same dirty-blue precipitate. If the reddish-white pre- 
cipitate is dissolved in pure nitric acid, and a solution 
of nitrate of silver is added to it, an abundant white pre- 
cipitate is produced, which, when washed, dried, and cal- 
cined, yields silver in the metallic state — a proof that the 
precipitate is cyanide of silver. The reddish-white preci- 
pitate is soluble in an excess of hydrochloric acid, in nitric 
acid, and in aqua regia ; it is also soluble in aqueous 
ammonia, and in a solution of cyanide of potassium. 

' 5. When a solution of silver, prepared for silvering arti- 
cles of bronze or of brass, has been employed a certain time 
for that purpose, the precipitate produced in it by the addi- 
tion of hydrochloric acid is not pure white, but reddish, in 
consequence of the reddish-white cyanide of copper which 
is precipitated with it : for we know that those silvering 
liquids which have been used for some time, contain copper 
in solution. The same thing occurs with the solutions for 
gilding, in which articles of silver, copper, bronze, and brass, 
have been gilded for a long time ; the liquid contains after a 
certain time of service, not only gold, but also silver and 
copper. This case presents itself especially when gilded 
articles of silver, containing copper, or other alloys of silver, 
are in the solution of gold ; then the precipitate of cyanide 
of gold produced by the addition of hydrochloric acid, does 
not possess its proper pure yellow colour. It has happened 
to me to observe a precipitate of this kind, which, instead of 
being yellow, was green, and, in fact, articles of iron had 
been gilded in the solution, and the precipitate contained, 
besides cyanide of gold, Prussian blue, so as to be demon- 
strated in an examination, which consisted in boiling the 
green precipitate in aqua regia, filtering to separate the dirty- 
green residue, evaporating the filtered liquid to dryness, and 
dissolving the dry salt in water acidulated with hydrochloric 



Recovering Gold and Silver from Old Solutions. 191 

acid ; the addition of sulphate of iron to this new liquid 
gave a brown precipitate, and the salts of tin a reddish-brown 
precipitate. In treating by aqua regia, the cyanide of gold 
was then decomposed, and converted into chloride of gold. 

' Based upon the preceding facts, we may find several 
methods for recovering all the silver and gold of old cyanide 
of potassium solutions. The extraction of these precious 
metals may be effected, either by the wet or by the dry process. 

' Extraction of silver by the wet method. — Adding hydro- 
chloric acid until the liquid exhibits a strongly acid reaction. 
The precipitate of chloride of silver which is thus obtained, 
will be, as we have already said, of a reddish-white colour, 
because of the cyanide of copper, which is precipitated with 
it, when the solution has been used a long time for silvering 
objects containing copper. In this precipitation by hydro- 
chloric acid, there is hydrocyanic acid gas set free, therefore 
the operation should only be performed in the open air, or 
in a place where there is good ventilation ; if the precipitate 
is very red, it must be treated with hot hydrochloric acid, 
which will dissolve the cyanide of copper. The chloride of 
silver, having been washed with water, must be dried, and 
then fused with pearlash in a Hessian crucible coated with 
borax, in the ordinary manner for obtaining metallic silver. 

' This method is very simple in its application, and very 
economical, considering, that by the aid of the hydrochloric 
acid, all the silver contained in the solution of cyanide of 
potassium is precipitated, and there remains no trace of it 
in the liquid. But the quantity of hydrocyanic gas which 
is disengaged, is a circumstance which must be taken into 
serious consideration when operating on large quantities of 
silver solution, the vapour of which is most deleterious, and 
nothing but the most perfect ventilation, combined with 
arrangements for the escape of the poisonous gases, will 
admit of the process being carried on without danger to the 
workmen ; when, however, we have taken the precautions 
dictated by prudence, the method in question may be con- 



1 92 The A rt of Electro-Metallurgy. 

sidered as perfectly practical. The liquid should be poured 
into very capacious vessels, because the addition of the acid 
produces a large amount of froth. 

1 Extraction of silver by the dry method. — The solution of 
cyanide of silver and potassium is evaporated to dryness, 
the residue fused at a red heat, and the resulting mass, when 
cold, is washed with water. The remainder is the silver in a 
porous metallic condition. There still remains in the wash 
waters a little silver, which may be precipitated by the addi- 
tion of hydrochloric acid. 

' Extractiofi of gold by the wet method. — A solution of gold 
and cyanide of potassium, which has long served for gilding 
articles of silver alloyed with copper, may still contain, as 
, we have already remarked, independently of the gold, both 
silver and copper, and perhaps iron. In order to obtain 
these metals we operate in the following manner : — 

' The liquid, the same as with the solution of silver, is 
acidulated with hydrochloric acid, in which case there is 
produced a disengagement of hydrocyanic acid gas, which 
requires the same careful ventilation. This addition of 
hydrochloric acid causes a precipitate, which may, according 
to circumstances, consist of cyanide of gold, cyanide of 
copper, and chloride of silver. The precipitate, washed and 
dried, is boiled in aqua regia, which dissolves the gold and 
copper in the form of metallic chlorides, and leaves the 
chloride of silver unaffected. The solution, containing the 
gold and the copper, is evaporated nearly to dryness, in 
order to drive off any excess of acid ; it is then dissolved in a 
small quantity of water, and the gold precipitated from it 
(by the addition of protosulphate of iron) in the state of a 
brown powder. The chloride of silver is reduced to the 
metallic state by the known means. The liquid from which 
we have precipitated the cyanide of gold, &c, by hydrochloric 
acid, may yet contain a little gold in solution. I refer to No. 
5 for its further treatment. 

This method is distinguished by the great simplicity of the 



Extraction of Gold from Old Solutions. 193 

operation, and we may repeat for it all that we have already 
said respecting the extraction of silver by the wet method. 

' Extraction of gold by the dry method. — The solution of 
cyanide of potassium which contains gold, silver, and copper, 
is evaporated to dryness \ the residue fused at a red heat, 
cooled, and washed (the wash waters still contain a little 
gold and silver, and this occurs most often when the solution 
of gold or silver contains a very great excess of cyanide of 
potassium). The residue, after washing, consists of gold and 
silver in a metallic porous state, and carbide of copper re- 
sulting from the decomposition of cyanide of copper by the 
heat. The metallic residue is treated with aqua regia, which 
forms insoluble chloride of silver, and contains the chlorides 
of gold and copper in solution. In order to obtain these 
bodies in the metallic state, we must proceed in the 
manner previously indicated. 

' If we operate according to the method of Professor 
Boettger, i.e. if we fuse the dried residue with its own volume 
of litharge, in a covered crucible, the regulus we obtain in 
this case, consists of gold, silver, and lead. In treating this 
alloy by nitric acid, of specific gravity 1*2, and applying 
heat, the gold remains in the form of a brown powder, 
whilst the lead and the silver are dissolved in the acid. This 
solution, after having been largely diluted with boiling dis- 
tilled water, may have the silver separated from the lead, by 
the addition of hydrochloric acid. 

' These methods of extracting the silver and gold, from old 
solutions of cyanide of potassium by the dry process, present 
this advantage, that the operator is not incommoded while 
working, by the disengagement of vapours of hydrocyanic 
acid. In these operations, the poisonous gases are not deve- 
loped as they are in the processes for extracting the metals 
by the wet method. 

1 After the experiments here reported, those who are 
interested in the subject, may choose for themselves, which 
of these methods appears the most suitable to the circum- 

o 



1 94 The A rt of Electro-Metallurgy. 

stances in which they are placed, and the object which they 
wish to obtain.' 

The process of recovering the silver from old plating 
solutions, depends largely upon the bulk of the liquid ; if that 
is small, the liquid may be evaporated to dryness, and the 
silver recovered by the dry method, taking care to ascertain 
that the fused salt above the button of silver, is free from 
precious metals, before throwing it away ; but if the bulk is 
great, the solution, contained in capacious vessels, must be 
precipitated by an excess of hydrochloric acid, added to it 
in the open air, taking extreme care not to breathe the vapour 
of hydrocyanic acid which is evolved. 

Testing the purity of silver. — The silver recovered from 
solutions, strippings, and residues, is often not pure ; that 
employed as anodes is sometimes not perfectly pure, and 
electro-deposited silver, although not often alloyed, is not 
necessarily pure, because in some cases, other metals are de- 
posited with it, in order to obtain the desired tint of colour. 

According to Dr. Bottger, the purity of silver may be 
ascertained as follows : — Apply, by means of a glass rod, a 
drop of cold saturated solution of bichromate of potassium, 
in nitric acid of sp. gr. 1*2, to a clean part of the surface, 
and immediately wash it off with cold water ; if the silver is 
pure, a blood-red mark is left. All other metals behave differ- 
ently from this ('Chemical News,' vol. xxiii. p. 119). Runge 
had also previously employed a somewhat similar test. He 
immersed the article in a cold mixture of thirty-two parts of 
water, four of sulphuric acid, and three of chromate of potash. 
The immersed part quickly assumed a purple colour, which 
was less deep and less lively, in proportion to the amount of 
alloy contained in the silver. 

Silver may be purified, by dissolving it in warm dilute 
nitric acid, immersing clean sheets of copper in the liquid, 
until all the silver is precipitated, finally making the solution 
quite warm, to complete the precipitation, or until a little of 
it gives no white cloud on adding to it two or three drops of 



Preparation of Salts of Mercury. 1 9 5 

hydrochloric acid. The liquid may then be thrown away, 
the metallic silver precipitate washed, dried, and melted, with 
the addition of a little carbonate of potassium, and a trace 
of saltpetre put with it into the crucible ; or the silver may be 
preserved for future use in making argentic nitrate. Silver 
may also be purified by dissolving it in nitric acid, then 
precipitating it by hydrochloric acid, and fusing the washed 
and dried chloride, with about one-half its weight of the an- 
hydrous carbonates of sodium and potassium, and a little 
saltpetre, in an earthen crucible. 

14. Mercury. — Elec. chern. eqt. = — = 100 The or- 

2 

dinary compounds of this metal, are the dioxide (red preci 
pitate), nitrate, mercurous chloride (calomel), bichloride or 
mercuric chloride (corrosive sublimate), bisulphide (vermi- 
lion), and bicyanide. The most soluble of these salts are 
the nitrate, bichloride, and bicyanide. 

Mercuric nitrate is made, by dissolving mercury in diluted 
nitric acid ; corrosive sublimate may be more conveniently 
purchased than made. The bicyanide is prepared, by add- 
ing eight parts of Prussian blue, and sixteen parts of mercuric 
oxide (red precipitate), (both in a state of fine powder,) to 
thirty parts of water ; boiling the mixture about fifteen 
minutes, filtering, evaporating, and crystallising the solution. 
It may also be made, by digesting an excess of red oxide of 
mercury, in the strongest aqueous hydrocyanic acid, until the 
odour of the acid has disappeared, and then evaporating the 
clear liquid. Also by dissolving one part of ferro-cyanide 
of potassium, in fifteen of boiling water, adding two parts 
of mercuric sulphate, digesting it hot for fifteen minutes, 
and then filtering the mixture, and crystallising the clear 
solution. Lielegg prepares it, by passing vapour of hydro- 
cyanic acid through water in which finely divided oxide of 
mercury is suspended ('Chemical News,' vol. xxvi. p. 264). 
About fifty-five grains of cyanide of mercury, dissolve in 
one ounce of water at 6o° Fahr. I have found that two 



1 96 The A rt of Electro-Metallurgy. 

and a half ounces of corrosive sublimate, converted into 
oxide of mercury, required about nine ounces of hydrocyanic 
acid of maximum strength (i.e. 'Scheele's strength,' see p. 
197) to dissolve it with the assistance of heat. The double 
cyanide of mercury and potassium may be made, by dissolving 
an equivalent of bicyanide of mercury in water containing an 
equivalent of cyanide of potassium in solution, and evapora- 
ting the clear liquid. A very dilute solution of this salt, is used 
for ' quicking ' the surfaces of articles of copper, brass, and 
german-silver, which are to be silver-plated. (See also p. 323.) 

Deposition of mercury by simple immersion process (see 
also p. 78). — From solutions of mercuric chloride, cyanide, 
or nitrate, aluminium deposits mercury ; forming an amalgam 
which decomposes water at 6o° Fahr., and rapidly oxi- 
dises and becomes heated in the air. Aluminium deposits 
mercury from a solution of mercuric chloride in alcohol ; also 
from one of mercuric iodide in potassic iodide (A. Cossa, 
' Watts' Dictionary of Chemistry,' 2nd Supplement, p. 54). 
From a solution of mercuric chloride, magnesium deposits 
calomel and mercuric oxide (Commaille, 'Chemical News,' vol. 
xiv. p. 188). Nearly all the base metals coat themselves with 
mercury by simple immersion in solutions of mercuric salts. 

Electrolysis of salts of mercury (see also p. 89). — Com- 
paratively little as yet has been done in the electrolysis 
of salts of mercury. A solution of any such salt may be 
electrolysed, by putting some mercury as an anode in the 
bowl of a tobacco pipe, thrusting a platinum wire down the 
pipe into the mercury, and immersing the bowl in the liquid • 
or the mercury may be placed in the vessel which contains 
the solution, and be connected with the positive pole of the bat- 
tery by a platinum wire passing through a tube of india-rubber 
to protect it from the liquid. Gladstone and Tribe have ob- 
served, that on passing a weak electric current through a solu- 
tion of mercuric chloride, into a cathode of platinum, a film 
of mercurous chloride is deposited ; but with a strong electric 
current, mercury itself is set free. I have noticed, that with 



Electrolytic Vibrations and Sounds. 197 

a mercury anode and platinum cathode, in dilute sulphuric 
acid, the cathode soon receives a coating of mercury on 
passing a current. 

Electrolytic vibrations and sounds. — As long ago as the 
year 180 1, Gerboin observed, that mercury exhibited 
peculiar movements whilst acting as an electrode in electro- 
lysis, and this phenomenon has been since investigated 
by Sir J. Herschel, Sir H. Davy, and others. According to 
G. Lippmann, the contraction of a globule of mercury, 
(whilst acting as a cathode in dilute sulphuric acid,) on the 
passage of the current, is due to a change in the capillary 
constant ('Journal of the Chemical Society/ vol. xi. p. 
1094). It was whilst investigating these peculiar move- 
ments, and searching for thermic changes in electrolysis, by 
passing an electric current through a solution of double 
cyanide of mercury and potassium, with mercury electrodes, 
that I first heard a faint sound, and then observed the 
surface of the mercury covered with waves ; and by further 
research, was led to the discovery of electrolytic sounds ; the 
dancing motion, and musical sound, being due to the alter- 
nate formation and destruction, of films upon the mercury, 
by electrolytic action. A paper on the subject in the 
'Proceedings of the Royal Society 7 1862, contains a full 
account of the phenomenon, and of the influence of various 
circumstances upon it. 

The best liquid for producing the sounds, consists of ten 
grains of cyanide of mercury, and 100 of pure hydrate of 
potash, dissolved in 2f ounces of aqueous hydrocyanic acid, 
containing 5 per cent, of the anhydrous acid (' Scheele's 
strength ') ; the liquid should be filtered. The phenomena 
usually occur only at the negative electrode , and out of 
a large number of solutions examined, the only ones in which 
phonetic vibrations occurred, were those of alkaline cyanides 
containing dissolved mercury. The quicksilver may be 
contained in two very small watch glasses submerged in the 
solution ; and the current, from either two Grove's, or five 




1 98 The A rt of Electro-Metallurgy. 

Smee's cells, conveyed to the electrodes by platinum wires, 
protected, except at the ends, from contact with, the liquid 
by means of tubes of glass or india-rubber. During the 
Fig. 27. occurrence of the sounds, the current itself is 

rendered imperfectly intermittent, and the 
arrangement may to a certain extent be em- 
ployed for similar uses to those of a break- 
hammer. A more perfect arrangement, con- 
sists of a glass vessel of the annexed form 
(see fig. 27), placed upon a sounding-board. 
One portion of mercury is poured into the 
centre, the other into the annular space, the wires immersed 
the two portions, and the liquid is above. 

CLASS IV. BASE METALS. 

COPPER — NICKEL — COBALT — IRON — MANGANESE CHRO- 
MIUM — URANIUM — TUNGSTEN — MOLYBDENUM — VANA- 
DIUM — LEAD — THALLIUM — INDIUM — TIN — CADMIUM — 
ZINC. 

15. Copper. — Elec.-chem. eqt = -AA = 3175. The 

2 

commonest salts of copper, are the suboxide, or cupreous 
oxide (red oxide of copper) ; the protoxide, or cupric oxide 
(black oxide of copper) ; the nitrate, chloride, sulphate (blue 
vitriol), cyanide, and acetate. The black oxide is made by 
heating the nitrate to full redness in a crucible, washing and 
drying the product. The sulphate is most conveniently 
purchased (its price is about sixpence per pound) ; or it 
may be made by heating copper filings in oil of vitriol until 
the product is nearly dry, washing the residue in boiling 
water, evaporating and crystallising the filtered solution. 
The chloride and nitrate may be formed, the first by dissolv- 
ing copper in aqua regia, or by saturating hydrochloric acid 
with protoxide of copper, and evaporating and crystallising 
the liquids ; and the second, by dissolving copper in nitric 



Electrical Relations of Copper. 199 

acid, evaporating and crystallising the solution. Acetate of 
copper is most conveniently purchased ; its commercial name 
is crystallised verdigris. Cyanide of copper may be made, 
by adding a solution of cyanide of potassium to one of 
sulphate of copper (each liquid being cold), just as long 
as a precipitate is produced, but no longer ; filtering and 
washing the precipitate, which is the required compound; 
it is a fine powder of a pale green colour. In the opera- 
tion, a large quantity of cyanogen gas is evolved, which 
if inhaled is dangerous to health. The powder contains 
two equivalents of cyanogen, for eveiy three equivalents of 
copper ; it is freely soluble in a solution of cyanide of 
potassium ; it is also soluble in aqueous ammonia, and in a 
solution of carbonate of ammonium. The liquid, after pre- 
cipitation, is invariably greenish blue, and contains much 
dissolved copper, but no use has hitherto been made of this 
remainder. Carbonate of copper may be prepared, by pre- 
cipitating a cold solution of cupric sulphate, by one of 
washing-soda ; it is a green powder. 

Electrical relations of copper. — Copper is electro-positive 
to iron in the following liquids at 6o° Fahr. : powerfully in 
a solution of sulphide of ammonium ; feebly in a saturated 
aqueous one of ammonia ; in a solution of oxide of copper 
in liquid ammonia, in aqueous ammonia, or in a saturated 
solution of ferro-cyanide of potassium, each but for a short 
time — it then becomes negative ; in a saturated solution of 
bichromate of potassium ; in a strong aqueous one of sul- 
phide of potassium, it is increasingly positive up to the boil- 
ing point of the liquid. This last liquid has a similar effect 
on brass. 

Deposition of copper by simple immersion process (see also 
p. 78). — From a solution of cupric sulphate, magnesium 
deposits the metal, its hydrated protoxide, and a green 
subsalt; but from one of cupric chloride, it precipitates 
Brunswick-green and no metal (Commaille, ' Chemical 
News,' vol. xiv. p. 188). Metallic aluminium immersed 



200 The Art of Electro-Metallurgy. 

in a similar solution, very slowly deposits copper ; and, 
in one of the nitrate, it slowly separates (after several 
days) a basic salt and metallic copper ; the reduction is 
quicker if an alkaline chloride is added. From a solution 
of the chloride, it quickly deposits copper, but from one of 
the acetate, the copper is more slowly separated (A. Cossa, 
'Watts' Dictionary of Chemistry,' 2nd Supplement, p. 
54). By adding crystals of silicon to melted black oxide 
of copper, I observed a sudden incandescence, which raised 
the temperature to a full white heat ; copper was also de- 
posited and melted to a red metallic bead, and could be 
hammered into a thin sheet. By heating to redness also, 
one part of fragments of magnesium and six of cupric 
fluoride, copper was separated. I have also observed, that 
crystals of silicon immersed in a solution of fluoride of 
copper containing free hydrofluoric acid, instantly coat them- 
selves with bright copper, and evolve gas. According to 
Smee, iron does not decompose a neutral solution of acetate 
of copper, nor alkaline ones of the ammoniuret, ammonio- 
nitrate, or ammonio-sulphate ; but decomposes a solution of 
oxide of copper in nitric acid. Raoult states, that gold in 
contact with copper, in either a cold or boiling, acid or 
neutral, solution of a salt of copper, receives no deposit of 
copper (' Journal of the Chemical Society,' vol. xi. p. 465). 

Electrolysis of salts of copper. — I have electrolysed 
fluoride of copper (fused at a bright red heat in a deep 
copper vessel), by means of a platinum wire helix as the 
anode, and a copper wire helix as the cathode, and a 
current from six Smee's cells. The conduction was copious, 
as if the fused salt conducted like a metal, and an acid 
vapour was evolved. No copper was deposited, and 
the anode was unaltered ; the cathode lost 3*35 grains 
in weight, by corrosion near the surface of the fused salt, 
and the copper vessel was similarly acted upon in several 
experiments, and caused to leak. It was evidently an 
instance of conduction by a liquid without electrolysis, as 



Electrolysis of Salts of Copper. 20 1 

with fused argentic fluoride. A solution of fluoride of copper 
in pure dilute hydrofluoric acid, with copper electrodes, 
conducted well, and yielded a good deposit of copper, with 
a current from a single Smee's cell. Fluoride of copper is 
insoluble in anhydrous hydrofluoric acid, but dissolves 
quickly in aqueous ammonia. 

If a feeble current be passed by means of copper elec- 
trodes, through a solution of chloride of copper dissolved in 
dilute hydrochloric acid, the anode becomes covered with 
snow-white crystals of cupreous chloride, and the cathode 
receives a thick deposit of loose, spongy copper (' Chemical 
News,' vol. xxii. p. 167). Gladstone and Tribe observed, 
that if a strip of platinum was connected with one of copper, 
and both were immersed in a solution of cupric chloride, the 
platinum became covered with a layer of insoluble cupreous 
chloride, also, that if such a solution was electrolysed by a 
feeble current with platinum electrodes, chlorine appeared 
at the anode, and cupreous chloride at the cathode ; but if 
the current was strong, metallic copper was also deposited 
upon the edges of the cathode. Smee states, that a solution 
of cupric chloride is less readily decomposed by an elec- 
tric current than the nitrate, but more readily than the 
sulphate, and that it is one of the worst liquids for the re- 
duction of copper, and the metal is apt to assume a very 
peculiar appearance. He also states, that the ammoniuret, 
acetate, and hyposulphite, offer no advantages ; that they are 
difficult to decompose, and require a current from several cells; 
also the ammonio-chloride is a bad solution, having a ten- 
dency to evolve hydrogen, and yield a spongy copper deposit ; 
that iodide of copper, dissolved in a solution of iodide of po- 
tassium, cannot be employed, because it liberates iodine ; that 
a copper anode is but little corroded in a solution of sulpho- 
cyanide of potassium, and the liquid does not contain much 
metal ; and the anode is very slightly acted upon in a solu- 
tion of the potassio-tartra'te. (Compare Eisner's statement, 
p. 209.) 



202 The Art of Electro-Metallurgy. 

Applications of electro-deposition of copper. — The purposes 
to which the electro-deposition of copper has been applied, 
are much more numerous than those of any other metal. It 
is sometimes used for protecting iron and steel from oxida- 
tion, also to form a basis for silvering and gilding upon zinc, 
iron, steel, tin, lead, Britannia-metal, &c. ; to the production 
of medallions, busts, and even colossal statues, and many- 
other works of art ; to the refining of crude copper on the 
large scale, the separation of the metal from cupriferous 
solutions ; to making copies of engraved, stereotype, and 
daguerreotype plates ; to the coating of leaves, flowers, fruits, 
insects, &c, with copper, for the purpose of ornamentation ; 
to the arts of glyphography, galvanography, and electro-tint 
printing ; corrosion of the anode by electrolysis, has also 
been applied in voltaic etching. Bank-notes ; postage 
stamps; playing cards; maps of the Ordnance Survey ; and 
the illustrated papers in which grocers and others wrap their 
goods, are printed from electrotype copper plates. 

Coating articles with copper by simple immersion process. — 
A vast number of articles of a common kind, to which it 
is desired to impart merely the appearance of copper, such 
as steel pens, iron and steel wire, &c, are coated with a film 
of copper, by simply immersing them in an acidulated and 
dilute solution of the sulphate, washing them thoroughly, and 
drying them quickly by rubbing them with hot sawdust. To 
effect this object, mix together one measure of hydrochloric 
acid, three of water, and a few drops of a solution of sul- 
phate of copper ; clean and immerse the iron, wash it, rub 
it with the cupreous liquid, and re-immerse it repeatedly, 
adding a few drops of the copper solution occasionally. 

According to O. Gaudain, articles of cast-iron, wrought 
iron, and steel, may be coated with copper, by dipping them 
into a melted mixture of chloride and fluoride of copper, with 
five or six parts of cryolite, and a little chloride of barium, 
contained in a plumbago crucible ('Journal of the Chemi- 
cal Society,' vol. xi. p. 955). To coat brass with copper, 



Separation of Copper from Cupriferous Liquids. 203 

Dr. C. Puscher directs us to dissolve ten parts of sulphate of 
copper, and five of salammoniac, in 150 of water. Immerse 
the previously cleaned articles in this liquid for one minute, 
drain them, and then heat them over a charcoal fire until 
the ammoniacal salt is expelled, and the coating of copper 
appears perfect, then wash them with water, and dry them 
(' Chemical News,' vol. xxiii. p. 215). 

M. Weis Kopp, deposits copper upon cast iron, by 
the simple immersion process, in a bath composed of ten 
parts of nitric acid, ten of chloride of copper, and eighty of 
hydrochloric acid of specific gravity 1*105. He immerses 
them several times, until a sufficient deposit is obtained, 
rubbing them with a woollen cloth between each immer- 
sion. The articles are first cleaned in a mixture of one 
part of nitric acid, and fifty of hydrochloric acid of specific 
gravity 1*105 ('Chemical News/ vol. xxi. p. 47). For 
coating iron wire with a film of copper by this method, 
Roseleur uses a mixture, composed of fifty to a hundred 
parts of water, one of sulphate of copper, and one of 
sulphuric acid ; and, if the deposit is not sufficiently adhe- 
rent, the copper is compressed by drawing the wire through 
a hole in a steel plate. He coats small articles, by burying 
them in sawdust wetted with this solution, diluted with three 
or four times its volume of water, and tossing the articles and 
sawdust about. 

Separation of copper fro?n cupriferous liquids. — Extremely 
large deposits of sulphide of iron, containing a greater or 
less percentage of cupric sulphide, exist in mineral strata. 
These sulphides, by exposure to air and water, become 
more or less oxidised into sulphates, and are rendered 
soluble. In this way, the water of certain mines becomes 
impregnated with sulphate of copper, and from very 
ancient times, copper has been separated in the metallic 
state from such waters, by immersing fragments of iron 
in them. Of late years, these immense deposits, (notably 
those of the Tharsis and Rio Tinto mines in Spain,) have 



204 The Art of Electro- Metallurgy. 

been worked by scientific processes, and all their constituents 
utilised. The sulphur contained in them is burned and con- 
verted into oil of vitriol, and has become one of the chief 
sources of supply of that acid. The sulphide of iron, con- 
verted into oxide by that process, is next mixed with common 
salt, and the mixture roasted, to render the copper soluble, a 
quantity of hydrochloric acid being at the same time produced 
from the common salt, and collected. By washing the roasted 
mixture with the dilute hydrochloric acid, and with water, 
all the copper is extracted as a greenish-blue liquid. This 
liquid is run into large vats filled with scraps of iron, and 
kept hot by passing steam into it. In a short time all the 
copper is reduced in the form of feathery crystals upon 
the iron, and falls to the bottom of the liquid as a red 
powder ; which is separated from the iron, and refined 
in the usual manner. The washed oxide of iron is 
employed as a source of metallic iron, and for ' fettling * 
furnaces. In this way, great quantities of copper are 
yearly obtained, and many hundreds of thousands of tons 
of a substance, for which there previously existed no uses, 
are beneficially utilised. The process usually employed, is 
the one patented by Mr. Henderson. 

Deposition of copper by contact with another metal (see 
also p. 82). — The electro-deposition of copper upon cast- 
iron fountains, lamp posts, &c. is very common in faris. 
The process of M. Fred Wiels, is as follows : — Dissolve 
in 1,000 parts of water, 150 of sodio-potassic tartrate, 
eighty of soda-lime containing from 50 to 60 per cent 
of free soda, and thirty-five of sulphate of copper. Iron 
and steel, and the metals whose oxides are insoluble in 
alkalies, are not corroded in this solution. The iron or 
steel articles, are cleaned with dilute sulphuric acid, of 
specific gravity i'oi4, by immersing them in that liquid 
from five to twenty minutes, then washed with water, and 
finally with water made alkaline by soda, then cleaned with 
the scratch-brush, again washed, and then immersed in the 



Coppering Cast-iron Cylinders. 



205 



cupreous bath, in contact with a piece of zinc or lead, or sus- 
pended by means of zinc wires ; the latter is the most economi- 
cal way. The articles must not be in contact with each other. 
They thus receive a strongly-adherent coating of copper, 
which increases in thickness (within certain limits) with the 
duration of immersion. Pure tin does not become cop- 
pered, by contact with zinc in this solution ; it oxidises, and 
its oxide decomposes the solution, and precipitates red sub- 
oxide of copper, and by prolonged action, all the copper is 
thus removed from the liquid. The iron articles require to 
be immersed from three to seventy-two hours according to 
the colour, quality, and thickness of the required deposit. 
The copper solution is then run out of the vat, and the 
coated articles washed in water, then cleaned with a 
scratch-brush, washed, dried in hot saw-dust, and then in a 
stove. To keep the bath of uniform strength, the liquid is re- 
newed from below, and flows away in a small stream at the 
top. After much use, the exhausted liquid is renewed, by 
precipitating the zinc by means of sulphide of sodium, 
(not in excess), and re-charging the solution with cupric 
sulphate. He also supplies to the bath, hydrated oxide of 
copper ('Chemical News,' vol. xiii. p. 1). 

By simple cell process. Coppering cast-won cylinders for 
calico printing. — M. Schlumberger's process. The cylinder 
(having been perfectly cleaned by the usual methods,) is made 
the cathode (with a current from four or six elements) during 
twenty-four hours, in a mixture of two liquids, composed of 



Water 


Parts 

. 12 


Water 


Parts 
. 16 


Cyanide of potassium 


• 3 


Sodic carbonate 


• 4 






,, sulphate . 


2 






Cupric ,, 


I 



It is then well washed, rubbed with pumice powder, then 
washed again with an aqueous solution of cupric sulphate, 
of specific gravity i'i6i, containing -^} )() part of its volume 
of sulphuric acid, scraps of copper being kept in the bath 



206 The A rt of Electro-Metallurgy. 

to supply the loss of copper, and prevent the liquid becoming 
too acid. It is immersed again in the above alkaline solu- 
tion, or else in a mixture composed of two liquids, viz. : — 



Parts 
Water . . . .10 
Cyanide of potassium . 3 

Aqueous ammonia . . 3 



Water 

Sodic carbonate 

„ sulphate . 

Cupric acetate . 



16 

4 

2 
2 



In these mixtures, at a temperature of 15 ° to 1 8° C, it is sur- 
rounded by porous cells containing zinc rods and dilute sul- 
phuric acid, and connected with the zinc by copper wires. 
The cylinders are turned partly round once a day, in order 
to render the deposit uniform, and the action is continued 
during three to four weeks, until the deposit is ^gth of an 
inch thick (G. Schaeffer, ' Chemical News,' vol. xxx. p. 219 ; 
' Journal of the Chemical Society,' vol. xiii. p. 196). 1 

Depositio?i of copper by separate cicrre?it process. — In de- 
positing copper by the single cell method, a nearly saturated 
solution of sulphate of copper answers very well, but for 
the battery process, an excellent solution may be made, by- 
dissolving four parts, by weight, of finely powdered sulphate 
of copper (best quality), and one of sulphuric acid, in 
about eighteen or twenty of water, and then filtering 
it ; neither of these solutions however, are fit to deposit 
copper upon steel, iron, or zinc, because the electrical rela- 
tions are unsuitable ; these metals decompose such liquids 
rapidly, and deposit the copper upon themselves by simple 
immersion. Some persons use a solution containing a 
smaller proportion of acid, a greater one of copper salt, and 
less water ; and others add a small quantity of sulphate of zinc 
or sulphate of potassium to the liquid ; the latter is very good. 

Deposition of copper upon metals. — The sulphate solu- 
tion is used for coating all metals and alloys, such as 
brass and german-silver, which do not decompose that 
liquid ; but zinc, iron, steel, tin, lead, Britannia-metal, type- 

1 See also H. Wildes, patent No. 4515, Dec. 28, 1875. 



Coppering Base Metals. 207 

metal, &c, which precipitate the copper from such a liquid 
by simple immersion, are coated in the cyanide or other 
alkaline solution ; and as the deposition of copper from an 
alkaline liquid is more expensive than that from the sulphate, 
if a greater thickness of metal is required, the additional 
thickness is put on the articles in the sulphate solution. 

Deposition of copper upon zinc, iron, &=c. — Various solu- 
tions are employed for this purpose, but they are all alkaline 
ones, and mostly contain cyanide of copper dissolved in 
cyanide of potassium. A very good one may be formed 
thus :— Dissolve cyanide of copper to saturation in water 
containing about two pounds of cyanide of potassium to 
the gallon, and then add about four ounces more of the 
potassic salt per gallon, to form free cyanide ; the liquid is 
then ready, and should be used at a temperature of about 
150° Fahr. Cyanide of copper is not very soluble in cyanide 
of potassium solution, the liquid formed, does not readily 
dissolve the anode, nor does it conduct well ; it also has a 
strong tendency to evolve hydrogen at the cathode, but this 
may be lessened, or wholly prevented, by avoiding the use of 
any free cyanide of potassium, employing a weaker current, 
and adding some aqueous ammonia and oxide of copper. 

Watt recommends a solution, composed of one gallon 
of water, six ounces of cyanide of potassium, four of 
carbonate of potassium, two of liquid ammonia, and two 
of cupric sulphate. Dissolve the sulphate of copper 
in rain water, and, when cold, add the carbonate 
of potassium, and the ammonia. When the precipi- 
tate is re-dissolved, add the cyanide. Decant the clear 
liquid for use. Another, recommended by Roseleur, is, 
to reduce twenty parts of crystallised cupric acetate to 
powder, and rub it to a paste with a little water, add to it 
200 parts of water containing twenty parts of dissolved 
washing-soda, and stir the mixture ; a light green precipitate 
is formed ; twenty parts of bisulphite of sodium are now dis- 
solved in 200 parts of water, and the solution mixed with 



208 The Art of Electro- Metallurgy. 

the former one ; the precipitate becomes dirty yellow. And, 
lastly, dissolve twenty parts of perfectly pure cyanide of 
potassium, in 600 of water, and add it to the previous 
mixture. If the solution is not quite colourless, add more 
cyanide until it is so. This liquid may be used either hot 
or cold, and requires a current of moderate strength. An- 
other very good liquid, which may be employed either hot or 
cold, consists of 2,500 parts of water, fifty of potassic 
cyanide of 70 per cent., thirty- five of acetate of copper, 
thirty of bisulphite of sodium, and twenty of aqueous 
ammonia. The cyanide and bisulphite, are to be dissolved 
in one part of the water, and the ammonia and acetate of 
copper in the other, and the two solutions mixed together. 
If the blue solution of acetate of copper in aqueous ammo- 
nia, does not then become quite colourless, a little more 
cyanide must be added. If these liquids are used hot, the 
deposition is more rapid. If they become green, or blue, by 
working, it is from an excess of copper dissolved, and either 
the anode should be reduced in size, or some cyanide of 
potassium added. And if the anode acquires a brown or 
white insoluble coating, the liquid is deficient in copper, and 
some of the solution of acetate of copper in ammonia, must 
be added. 

A good depositing solution, for coating iron and steel by 
the battery process, may be made, by dissolving ammoniuret 
of copper in a solution of cyanide of potassium. Nine 
hundred or 1,000 parts of water, containing eighty parts 
of cyanide of potassium, dissolve forty parts of the blue 
ammoniuret, and form a colourless liquid. 

W. H. Walenn's solution for coppering iron, consists of 
cyanide of copper dissolved to saturation, in a solution of 
equal parts of potassic cyanide, and ammonium tartrate, and 
sufficient oxide of copper, and ammoniuret of copper added, 
to prevent evolution of hydrogen at the surface of the arti- 
cles. The solution is used at 8o° C. (=176° Fahr.). In 
this process, one Smee's cell may be employed. The cost 



Management of Copper Solutions. 209 

has been found to be about 2s. 6d. per pound of metal depo- 
sited. One ounce and a half of copper per square foot will 
protect iron from rust ('Chemical News,' vol. xxi. p. 247; 
vol. xxii. p. 181). 

Dr. Eisner coats base metals with copper, in a solution 
made as follows : — One part of bitartrate of potassium in 
powder, is boiled in ten parts of water, and as much freshly 
prepared, and wet hydrated carbonate of copper (which has 
been washed with cold water), stirred with it, as the liquid 
will dissolve. The beautiful dark blue alkaline liquid is fil- 
tered, and rendered still more alkaline by addition of a 
small quantity of carbonate of potassium. A copper anode 
dissolves readily in the liquid (compare Smee's statement, 
p. 201), and the solution may be employed to coat objects 
composed of tin, cast iron, and zinc (' Chemist,' vol. vii. 
p. 124). 

Management of copper depositing liquids. — Sulphate of 
copper depositing solutions are the most easy of any to 
manage, because the range within which the density of the 
current may be varied, without causing a bad deposit, is 
greater than with those of any other metal, not even except- 
ing antimony ; much however, depends with copper, as 
with other metals, upon the kind of liquid employed ; many 
cupreous solutions are difficult to manage, and none are 
as easy as the sulphate ; the alkaline ones, employed for 
coppering iron, etc., are much more difficult to obtain a 
thick deposit from, than the sulphate. 

The general rules which determine and regulate the quality 
of other deposited metals, operate also with copper ; if the 
current is too great in relation to the amount of receiving 
surface, the metal is set free as a brown or nearly black 
metallic powder, and hydrogen gas may even be deposited 
with it and evolved. In the sulphate solution, if the liquid 
is too dense, streaks are apt to be formed upon the receiving 
surface, and the article (especially if a tall one) will receive 
a thick deposit at its lower part, and a thin one at the 

p 



2 1 o The A rt of Electro-Metallurgy. 

upper portion, or even have the deposit on the upper end 
re- dissolved. If there is too little water, crystals of sulphate 
of copper form upon the anode, and sometimes even upon 
the cathode, at its lower part, and also at the bottom of 
the vessel. If there is too much acid, the anode is cor- 
roded whilst the current is not passing. The presence of a 
trace of bisulphide of carbon in the sulphate solution will 
make the deposit brittle, and this continues for some time, 
although the solution is continually depositing copper ; in 
the presence of this substance, the anode becomes black, but 
:f there is also a great excess of acid, it becomes extremely 
bright. Solutions of cupric sulphate, containing sulphate of 
potassium, and the bisulphide of carbon applied to them, 
are sometimes employed for depositing copper in a bright 
condition. The copper obtained from the usual double 
cyanide of copper and potassium solution, by a weak current, 
is of a dull aspect, but with a strong current it is bright. 

Rapidity and cost of depositing copper. — If a good sul- 
phate solution, and a strong current are employed, a thick- 
ness of \ of an inch of firm copper can be deposited, either 
by the single cell, or the separate current process, in about 
seven to ten days. The cost of copper deposited by a 
current from a battery, is usually estimated at 2s. or 2s. 6d. 
rer pound, but upon the large scale, by means of currents 
fiom magneto-electric machines driven by steam power, ob- 
tained under the most economical circumstances —as, for in- 
stance, by waste heat from other processes — it is probably 
less than 2d. per pound, exclusive of the value of the metal. 

Composition of the dirt upon copper anodes. — Everyone 
who has deposited copper from the sulphate by electrolysis, 
has observed how black and dirty the anodes become, be- 
cause he has been obliged to frequently wash them. Max, 
Duke of Leuchtenberg, analysed this black matter and found 
in it — 



Analysis of Dirt from Anodes. 



211 



Tin 33'5o 

Oxygen 24-82 

Copper 9-24 

Antimony . . . . . . .9*22 

Arsenic ....... 7*20 

Silver ....... 4*45 

Sulphur 2*46 

Nickel 

Silica 

Selenium ...... 

Gold 

Cobalt 

Vanadium ...... 

Platinum ...... 

Iron ....... 

Lead 



226 

1-90 

127 

-98 

-86 

'64 

-44 

'30 

-15 

99^9 
(See Erdmann's ' Journal of Practical Chemistry,' vol. 

xlv., 1848, pp. 460-468.) 

The following analyses of similar residues have been 

kindly supplied to me by a friend : — 



No. 


I. 




No. II. 




Copper 




85-850 


Lead . 


27-70 


Water and oxygen 


4-950 


Water and oxygen 


21 05 


Arsenic 


. 


2*480 


Copper 


19-40 


Silver . 


. 


I-8l 5 


Antimony . 


7-35 


Sulphuric acid 


. 


I-I50 


Sulphur 


6-35 


Insoluble earthy 


matter 


0-950 


Silver . 


. 5-61 


Antimony . 


. 


•750 


Arsenic 


5'20 


Iron 


. 


•750 


Earthy matter 


4-35 


Bismuth 


. 


•650 


Bismuth 


1-25 


Alumina 


. 


•250 


Chlorine 


•70 


Chlorine 


. 


'250 


Iron . 


•60 


Gold . 


. 


•085 


Nickel 


•20 


Lead . 


. 


•050 


Organic matter 


•20 


Loss . 


. 


•020 


Gold . 


•01 






ioo-ooo 


Loss . 


03 


Per ton of 20 cwt. 






IOOOO 


ozs. dwts 


grs. 




Per ton of 20 cwt. 




Silver = 623 2 


8 




Silver = 1835 ozs. 




Gold = 27 15 


8 




Gold = 3 ozs. 





P 2 



2 1 2 The A rt of Electro- Metallurgy. 



No. III. 

Copper .67-90 

Sulphur 18-10 

Iron 5-55 

Insoluble earthy matter . . . .3-40 
Organic matter . . . . . .2*25 

Lead 2*05 

Silver 0*55 

Loss . . . . . . . -20 

ioo-oo 

Refining crude copper by means of electrolysis. — The fore- 
going analyses throw great light upon the question, why it 
is, that electro-deposited copper (and also that found in the 
metallic state in fissures in rocks at Lake Superior, and other 
places, 1 ) is so very pure ; and also upon the process of re- 
fining crude copper by electrolysis. Several hundreds of 
tons of copper, are yearly refined by Mr. James Elkington's 
patent process (' Chemical News,' vol. xxi. p. 264). This 
simply consists in making large slabs of the crude metal (ob- 
tained from the ores by the usual melting process), the anodes 
in the ordinary sulphate of copper depositing liquid, and 
passing electric currents from numerous magneto-electric 
machines through them and the liquid ; a ' compound depo- 
siting vessel' (see pp. 24, 90) and a series of electrodes 
being employed. The copper dissolves, and nearly all the 
impurities are separated, and fall to the bottom as a dirty 
powder. The impurities vary of course, with the composition 
of the crude metal, and the success of the process depends 
largely, upon the selection of such crude metal as contains 
no such substances, as would be electro-deposited along with 
the copper. 

In this process, the metalloids, such as oxygen, sul- 
phur, selenium, phosphorus (and perhaps arsenic), carbon, 

1 A mass of copper, estimated to weigh between 75 and 100 tons, 
was discovered at Eagle Harbour, Lake Superior. 



Refining Copper by Electrolysis. 2 1 3 

boron, and silicon, are not liberated at the cathode. Any 
silver present, will not dissolve, because the sulphuric acid 
employed, contains a little hydrochloric acid, which converts 
it into insoluble chloride. Gold, if traces of it are present, 
is also insoluble. Lead is converted into sulphate, which is 
its most insoluble compound, and the small portion which 
does dissolve, is not deposited, because lead is electro-posi- 
tive to copper, and therefore copper is deposited first. 
Carbon, together with any sulphides present, also falls to the 
bottom as an insoluble powder. Iron dissolves, but being 
highly electro-positive to copper in such a liquid, is not 
deposited, even when present in very great amount. Zinc 
is probably not present, but, if it is, behaves like iron, and is 
more highly electro-positive. Tin is probably not dissolved, 
and if it were, being positive to copper, would not be de- 
posited. Cobalt behaves like iron, but the quantity present 
is very minute. Nickel dissolves, and if in very large 
quantity, would be deposited to a small extent along with 
the copper, but its proportion is also very small. Antimony 
(and perhaps also arsenic to a less extent) would be the most 
likely metal to contaminate the deposit. 

Analytical estimation of copper i?i alloys and ores by means 
of electrolysis. — In consequence of the possibility, by attend- 
ing to proper precautions, of depositing copper alone from 
a solution of its sulphate containing other metals, attempts 
have been made to separate the whole of the copper from 
those metals by such a process, and thus determine its 
amount, and a premium of 300 thalers, or 45/., was offered 
by the directors of the Mansfield copper mines, in Germany, 
for a satisfactory method. The successful competitor was 
Mr. C. Luckow, chief chemist to the Cologne-Minden Rail- 
way Company. The process is extensively used, and a full 
description of it may be found in the ' Chemical News/ vol. 
xix., 1869, p. 221. (Seealso Watts's 'Chemical Dictionar>,' 
2nd supplement, p. 384.) J. M. Merrick has also electro- 
lysed known weights of pure sulphate of copper in aqueous 



214 The A, rt of Electro- Metallurgy. 

solution, in a covered platinum crucible, with a platinum 
wire for the anode, and the crucible for the cathode, with a 
current from two or three Grove's cells, until all the metal 
was deposited, and then weighed the deposits. In two experi- 
ments, the percentages of copper obtained, were 25*44, and 
25*46, theory requiring 25*46 per cent. The deposits were 
washed with alcohol and cautiously dried (' Chemical News,' 
vol. xxiv. pp. 100-172). 

Preventing adhesion of deposit. — In all cases where a per- 
fect copy is required of a metal plate, or other metallic ob- 
ject, the surface to receive the deposit, must be sufficiently 
clean to enable the electricity to freely enter, but not so per- 
fectly unstained as to cause the deposit to adhere so firmly 
that it cannot be separated. To prevent adhesion, the metal, 
after having been cleaned and dried, should remain exposed 
some time to the air before being put into the depositing 
liquid ; it should also not be heated immediately before im- 
mersion ; and if a wire has to be soldered to it, that should 
be done beforehand. It should also not be put into the 
solution without first making all the connections of the cir- 
cuit complete, and attaching it to the battery, otherwise 
the momentary immersion may corrode and clean its surface. 
To make perfectly certain of preventing adhesion, without 
preventing a deposit, the dry surface of the metal may be 
brushed with a thick camel-hair brush with short hairs, and 
some fine black-lead, before immersion, in addition to taking 
the above precautions. In some cases, the articles to be 
copied, are rubbed with cotton wool slightly moistened with 
a very weak solution of beeswax, prepared by dissolving a 
fragment of wax of the size of a pea in a quarter of a pint 
of spirit of wine. In other cases they are rubbed over with 
a little olive-oil, and then wiped as clean as possible by 
rubbing with cotton- wool. To prevent adhesion of de- 
posits on copper, or on steel, vapour of iodine is also 
employed. 

Copying engraved copper-plates, medallions, 6°<r. — En- 



Preventing A dhesion of Deposits. 2 1 5 

graved steel plates, are copied by coating (' stopping off') the 
back and edges with copal varnish, allowing the varnish to 
become perfectly dry ; immersing the plate in the cyanide 
coppering liquid, and depositing a thin film of metal upon 
it, then washing it well, and at once suspending it in the 
sulphate of copper solution, and depositing the desired thick- 
ness; this will require from twenty-four to forty-eight hours. 
The surface of the steel should be previously prepared for 
a non-adhesive deposit, otherwise the two metals cannot be 
separated. If the plate to be copied, is a copper, brass, 
silver, or gold one, it lmy receive the entire deposit in the 
sulphate solution. Medallions and other forms of metal, 
may also be copied in a similar manner. As the metal in 
all such cases, has a great tendency to be deposited upon 
the edges, the deposit creeps round those parts, and this 
superfluous copper has to be filed off before the two can be 
separated. When they are taken apart, their surfaces are 
found to be perfectly dry. 

Copying Daguerreotype pictures in copper. — First sclder a 
wire to the back of the plate near the edge ; varnish the back 
and edges, and allow it to dry ; hang it (taking the above 
precautions) in a clean sulphate of copper solution, which is 
perfectly free from dust or grease on its surface, and in the 
course of twenty or thirty hours (if about two pairs of Smee's 
batteries have been used), the deposit will be sufficiently thick 
to be removed ; it should then be taken out, w r ell washed, 
wiped perfectly dry, and a narrow strip cut off its edges 
with a strong pair of scissors or shears ; the two may then 
be easily separated by inserting the blade of a knife, or the 
end of a thin wedge of hard wood, between them at the 
edges. If the process has been carefully managed, and the 
original picture is a strong one, a most beautiful and vivid 
copy will be obtained ; and if the picture is not only a 
strong one, but has been fixed by Fizeau's process, a number 
of successive copies may be taken from it, but their inten- 
sity, as well as that of the original, diminishes in each sue- 



216 - The Art of Electro-Metallurgy. 

ceeding trial. With a vivid original picture, clear solution, 
very regular and undisturbed action of the battery, and a 
fine deposit, there may be observed a most strange pheno- 
menon; it will be found that the picture has not entirely 
disappeared, even in twenty hours, although the coating of 
copper has constantly increased in thickness ; the image has 
penetrated quite through the deposited metal, and appeared 
upon the back, even with deposits as thick as an address 
card. In some cases the figure is optically positive, and in 
others negative. 

Copperi7ig doth. — Mr. J. Schottlaender took out a patent, 
Dec. 8, 1843, for depositing either plain or figured copper 
upon felted fabrics. He passes the cloth under either a 
plain or engraved copper roller, horizontally immersed in a 
sulphate of copper solution, (not containing much free acid,) 
and a deposit takes place upon the roller as it slowly revolves ; 
the meshes of the cloth are thus filled with metal, and the 
design of the roller copied upon it; the coppered cloth is 
slowly rolled off, and passed through a second and closely 
contiguous vessel filled with clean water. The roller is pre- 
viously prepared for a non-adhesive deposit. 

Deposition of copper upon non-metallic surfaces.— A suffi- 
ciently large conducting wire of copper is first attached to 
the object, and, if necessary, a number of 'guiding wires ' 
formed of very fine brass wire, are attached to the main wire, 
and their free ends stuck into the surface of the article, in 
those parts only where deposition is the most difficult to 
effect, such as in recesses or deeply undercut parts of 
the mould, which are the most distant from the anode, 
or into which exhausted portions of the solution, would 
ascend and collect. All light moulds and articles, require 
to be weighted, in order to make them sink in the so- 
lution ; lead is usually employed for this purpose. 

To deposit copper (or other metal) upon non-conductors, 
their surfaces must be rendered conductive. To effect this 
object, there are two methods in use : first, to cover them with 



Coppering Non-Metallic Surfaces. 21^ 

a thin film of black-lead, or the finest quality of metallic 
bronze-powder, by brushing ; or, second, to coat them with 
a minute film of gold or silver, by chemical means. The 
first of these methods is generally used for moulds com- 
posed of gutta-percha, wax, resinous composition, or plaster 
saturated with oil, where the parts are not much undercut ; 
the second for elastic moulds, because they will not bear 
the friction of black-leading, and because the black-lead can- 
not be readily applied to all their recesses. 

In employing black-lead, care should be taken to select 
a kind which conducts electricity freely ■ and this can only 
be found by actual trial. Some specimens conduct very 
badly, and others very well. It should be applied to the sur- 
face, by persistent brushing with a camel-hair brush, having 
a large and thick body of short hairs; breathing upon the 
face of the article occasionally, to facilitate the adhesion of 
the black-lead, and when the surface is perfectly black and 
bright, blowing off the superfluous powder. The whole 
operation occupies about ten or fifteen minutes with a small 
object the first time of preparing it, but less in subsequent 
operations with the same surface. A small quantity of black- 
lead is sufficient for a very large surface. The conducting 
power of black-lead is greatly improved by gilding or sil- 
vering it. It may be gilded as follows : — Dissolve one part 
of chloride of gold in ioo parts of sulphuric ether in a bottle, 
add fifty parts of the plumbago, mix them thoroughly, and 
expose the mixture in the open bottle to sunlight, stirring it 
frequently until it is perfectly dry ; apply it by brushing. 

A plan which I have devised, and which is cheaper than 
this, is to mix with the black-lead, one-third of its weight of 
the finest white bronze-powder. The particles of this pow- 
der, being composed almost wholly of tin, when immersed 
in a solution of sulphate of copper, dissolve, and coat them- 
selves with copper by the simple immersion process, and 
also cause those of black-lead in contact with them to be- 
come coated, and thus a thin deposit of copper is very 



2 1 8 The A rt of Electro-Metallurgy. 

quickly formed all over the bronzed surface. This effect 
will of course take place without connecting the mould 
with the battery, but they may be immediately connected 
together, and a deposit will spread over the whole of the 
bronzed surface by the ordinary battery process, through 
the medium of the bronze and the thin deposit already men- 
tioned, and it may be continued to any required thickness in 
the usual way. By this plan, gutta-percha medallions were 
repeatedly covered with a deposit of copper, in from two to 
five minutes, which would occupy from twenty to forty-five 
minutes when prepared by black-lead in the usual manner. 
The addition of white or tin bronze, causes the deposit to 
spread as rapidly as when the surface is prepared by the 
phosphorus solution, but without the disadvantage which 
occurs in using the latter, of making the deposited metal 
brittle. Silver may be deposited nearly as easily as copper 
upon black-leaded surfaces, but it must be remembered that 
wax moulds are injured in a cyanide of potassium solution, 
and should be protected by a layer of copal varnish on the 
parts not to be coated. 

For moulds of elastic composition, the depositor may 
employ the following liquids, patented by Mr. Alexander 
Parkes : A, the phosphorus solution : to make nearly three 
ounces of this, melt sixty-four grains of beeswax or tallow ; 
then dissolve eight grains of india-rubber (cut up very small), 
in 1 60 grains of bisulphide of carbon, and when it is dissolved, 
add to it very carefully (as it is highly inflammable) the 
melted wax, and stir the mixture thoroughly ; then dissolve 
sixty-four grains of phosphorus, in 960 grains (about two and 
a quarter ounces) of bisulphide of carbon, and add to it 
eighty grains of spirit of turpentine, and sixty-four grains of 
asphalte in fine powder ; when they are dissolved, add this 
solution to the previous one of india-rubber and wax, and 
thoroughly mix them by shaking. B, the silver solution : 
dissolve thirty grains of nitrate of silver in a pint (twenty 
ounces) of distilled water. And, C, the gold solution— to 



Preparing Non-Metallic Surfaces for Deposits. 219 

make twenty ounces of which, dissolve five or six grains of 
pure gold, in about twenty or twenty-five grains of a hot 
mixture, of one measure of nitric acid, and two or three 
of hydrochloric acid, and when dissolved, dilute the solution 
with twenty ounces of distilled water. 

In making surfaces conductive by this plan, the article, 
after the conducting and guiding wires are attached to it, is 
either dipped into the phosphorus solution, or its surface is 
covered with that liquid; and after it has been drained, 
it is allowed to remain until perfectly dry ; the silver solution 
is next applied to it, and is drained away in like manner for 
several minutes, until the surface acquires a metallic lustre like 
black china; it is then gently rinsed with distilled water, and 
the gold solution applied in the same way, which gives it a 
yellowish aspect: after another rinsing in distilled water, it is 
ready for receiving a deposit. 

The same patentee, includes in his patent a phosphorus 
moulding composition, by the use of which the immersion 
in the phosphorus liquid, is dispensed with, the moulds 
themselves containing the required amount of phosphorus. 
To make about one pound of this composition, melt together 
half a pound each of wax and deer's fat, then dissolve nine- 
teen or twenty grains of phosphorus in about 300 grains of 
bisulphide of carbon ; keep the wax mixture barely melted, 
and add the phosphorus solution slowly to it, with brisk 
stirring of the fat, pouring it in at the bottom of the melted 
mixture by means of a vessel with a long spout, to prevent 
its inflaming. It is highly dangerous to have spilt portions 
of the phosphorus composition or solution in contact with 
wood, paper, rags, etc., or other fibrous or porous substances, 
as after a lapse of some time (even hours), they will often 
burst into flame. 

Another method of rendering the surface of the article 
conductive, is to wet it with a solution of nitrate of silver, 
and then expose it to sulphuretted hydrogen gas ; this con- 
verts the film of silver salt into a conducting substance, viz., 



220 The A rt of Electro-Metallurgy. 

sulphide of silver ; the liberated nitric acid should then be 
removed, by dipping the article in distilled water. Or, wet it 
either with nitrate of silver or chloride of gold solution, and 
then expose it to hydrogen gas; this reduces the salts to 
metals. The article must then be rinsed. The film of silver 
salt may also be reduced to metal, by placing the object in a 
well closed box, containing at its lower part a porcelain dish 
containing a small quantity of a strong solution of phosphorus 
in bisulphide of carbon. In a few hours the vapour will re- 
duce the salt to a film of black silver. 

Non-conducting surfaces may also be rendered conduct- 
ive by washing them, first, with a mixture composed of equal 
parts of white of egg, and a saturated solution of common 
salt ; second, with a strong solution of argentic nitrate, and 
exposing them to sunlight until they are quite black ; and, 
third, with a saturated solution of green vitriol. (R. Piffard, 
' Chem. News,' vol. ii. p. 323.) Or by coating the surface 
with a film of gum -water, and drying; then with a solution of 
the nitrate, and drying ; and then exposing it to sulphuretted 
hydrogen gas. (R. Piffard, ' Chem. News,' vol. hi. p. no.) 

Hockin recommended, for metallising the surfaces of 
non-metallic bodies, to plunge them into iodised collodion, 
then immerse them in a nitrate of silver solution, expose 
them to the light for a few seconds, and then precipitate the 
silver in a metallic state by means of a bath of protosulphate 
of iron acidulated with nitric acid, and finally deposit copper 
upon them in a nearly neutral solution of cupric sulphate. 
('The Chemist,' New Series, vol. i. part 4, January 1854, 
p. 196.) Liquids used for dyeing hair black, composed of 
a solution of ammonio-nitrate of silver, followed by one of 
pyrogallic acid, might be similarly employed. 

In preparing a gypsum mould, Professor Heeren soaks it 
in wax, then covers it thickly with a mixture of a solution of 
one gramme of argentine nitrate, dissolved in two grammes 
of water, to which two and a half grammes of aqueous 
ammonia is next added; and then also three grammes of 



Preparing Non-Metallic Surfaces. 221 

absolute alcohol. The mould is then exposed to sulphuretted 
hydrogen gas. By employing four or five Daniell's cells, the 
copper spreads quickly. (' Journal of Chemical Society,' 
vol. x. p. 1 133.) 

Berland prepares non-conducting surfaces for receiving a 
deposit thus : — Wet the article with spirit of wine, wash it 
with distilled water, and whilst wet, pour over it a solution 
of one part of nitrate of silver in four parts of distilled water. 
After draining it a few minutes, a solution of one part of pure 
green vitriol in three parts of distilled water is poured upon 
it. After five minutes, repeat with the silver solution, and 
then with the green vitriol, three or four times, till the surface 
of reduced silver has a whitish-grey colour. Then wash it 
with pure water, and it is ready to receive the deposit. At the 
first moment of immersion, the entire surface is covered with 
a thin layer of copper (' Philosophical Magazine,' fourth series, 
vol. xxx. p. 451. See also Alexander Jones's patent, 1841). 

Coppering lamp-posts, cW. — M. Oudry electro-deposits 
copper upon gas-lamps, pillars, candelabras, fountains, and 
ornamental ironwork generally. He first coats the articles with 
a kind of red paint containing benzine, then black-leads the 
dried paint, and deposits copper upon it to the thickness of one 
millimetre, during four and a half days, by the battery process. 
The copper is afterwards bronzed by applying a solution of 
ammonio-acetate of copper. 

Coppering fruit, flowers, insects, reptiles, &>c. — Objects of 
this kind, some of which will scarcely bear handling, are 
first coated with silver by means of a saturated solution of 
argentic nitrate in hot alcohol. The nitrate is reduced to fine 
powder in a mortar, and an excess of it digested with alcohol 
in a flask placed in warm water, with occasional shaking, 
until the liquid is saturated. One hundred parts of alcohol, 
dissolve about two and a quarter parts of the salt. The articles 
are then dipped for a moment in the warm solution, and the 
liquid, being volatile, soon evaporates. The film of salt left 
upon the objects, is reduced to metal by either of the means 



222 The A rt of Electro-Metallurgy. 

already described ; the articles then coated in the solution of 
cupric sulphate, and either silvered or gilded as may be desired. 

E. T. Noualhier and J. B. Prevost. in their patent of 
January i, 1857, propose to ' metallise soft surfaces — a human 
corpse, for instance — by the following process : — All the 
apertures are stopped with modeller's wax, the body is placed 
in a suitable attitude, and pulverised nitrate of silver spread 
over it by means of a brush or otherwise ; it is then electro- 
coppered in a bath of sulphate of copper ; ' the ' result being 
a metallic mummy/ 

Coating plaster models and clay figures with copper. — Busts, 
and other similar objects, may be coated by saturating them 
with linseed-oil (or better, with beeswax), then well black- 
leading, or treating them with the phosphorus, silver, and gold 
solutions, attaching a number of ' guiding wires,' connected 
with all the most hollow and distant parts, and then immersing 
them in the sulphate of copper solution, and causing just suffi- 
cient copper to be deposited upon them by the battery process 
to protect them, but not to obliterate the fine lines or features. 

Copying wood engravings in copper. — This process is largely 
used. In cases where a great number of impressions of a 
particular woodcut is required, the plan of taking copies of 
the engraved wooden block in copper by the electro process, 
and using those copies instead of the original block to print 
from, has attained a considerable degree of importance ; the 
vignette at the head of the title-page of the ' Illustrated 
News,' the title-page of ' Punch,' many of the large engrav- 
ings in the ' Illustrated News,' and even the illustrations of 
some of the penny periodicals, are regularly produced in this 
way. To copy an engraved wooden block, the surface is first 
either black-leaded, or moistened with water, and firmly sur- 
rounded by a shallow frame of metal ; a thick piece of gutta- 
percha, more than sufficient to fill the enclosed space, and 
made quite soft by heat, is then laid upon it, commencing its 
contact at the centre of the engraving, and proceeding out- 
wards, so as to exclude all air-bubbles ; a plate of cold iron is 



Copying Wood Engravings. 223 

then laid upon the gutta-percha, and the whole subjected to 
gradually increasing pressure as the substance cools. The 
block and its copy are then separated, and the figured surface 
of the copy (with the main connecting wire previously attached) 
is treated in the usual manner, with black-lead (or with the 
phosphorus, silver, and gold solutions) ; ' guiding-wires ' are 
then affixed, and copper deposited upon the mould in a 
solution of sulphate of copper, until a moderate thickness 
of deposit is obtained, which will occupy at least twelve or 
eighteen hours ; when sufficiently thick, the deposit is re- 
moved, its back made rigid by a layer of solder or type 
metal (the surface being previously moistened with a solu- 
tion of chloride of zinc, to make the solder adhere), the back 
is planed flat, and mounted upon a block of w T ood to the 
height of the type. In London this process is employed 
upon a large scale, some of the copies being upwards of two 
feet square. Engravings upon steel are copied in an exactly 
similar manner. In some instances, successful deposits of 
large ' Illustrated News ' engravings, have been formed and 
taken off in eight hours ; but this can only have been effected 
by the most perfect black-leading, keeping the solution in 
excellent condition, and working it with the maximum of 
battery power. A mould of electrotype copper of the ' Times ' 
newspaper is said to have furnished as many as twenty 
millions of impressions before it was quite worn out. 

Copying set-tip type in copper. — The process of electrotyp- 
ing has been gradually encroaching upon that of stereotyping, 
and has, we are informed, almost superseded that process in 
America. The plan adopted, is similar to that of copying 
woodcuts, viz., to lay a sheet of softened gutta-percha upon 
the surface of the page of type (which is previously black- 
leaded), and subjecting it to increasing pressure until it is 
cold; the gutta-percha copy is then removed, and treated as in 
copying wood engravings. The advantages of electrotyping 
over stereotyping are numerous: the metal is harder, takes a 
sharper impression of the mould, and delivers the ink much 



2 24 The A rt of Electro-Metallurgy. 

more rapidly than type metal, besides being a cleaner 
process ; it also takes up less ink, and consequently the 
printed pages dry more quickly. Both woodcuts and letter- 
press, have also been copied in plaster of Paris, and the 
deposit of copper formed upon that ; but this material is 
much inferior to gutta-percha for the purpose. In deposit- 
ing copper upon moulded surfaces of set-up type, the deposit 
is thin, and easily broken, where there are lines ; to prevent 
this, the lines are wetted with a solution of nitrate of mercury, 
or other ' quicking' liquid (see pp. 195, 323), at those parts, 
and then deposited upon again. 

Moulding, and copying coins, cVr. — Some electro-de- 
positors confine themselves to multiplying printing surfaces, 
some to plating with nickel, others to plating with silver and 
gilding, to which latter process in other establishments, is 
added the multiplication of works of art, the production of 
busts, statues, &c. The electro-depositor, therefore, who 
includes in his business the multiplication of works of art, 
as well as the simple plating of metal articles, will require a 
knowledge of the art of moulding. 

Ability to reproduce works of art on a large scale, 
requires very considerable experience, and amateurs should 
first acquire ability to copy smaller ones, such as medals, 
coins, etc. The moulding materials commonly used for 
small objects, are fusible alloy, wax, stearine, gutta-percha, 
plaster of Paris ; a mixture of gutta-percha and marine glue, 
a composition of spermaceti, etc., etc. 

Fusible alloy, consists of a melted mixture of eight parts 
bismuth, five of lead, and three of tin, and fuses at 
about the temperature of boiling water. A much more 
fusible mixture, which melts at 15 1° Fahr., consists of seven 
and a half parts of bismuth, four of lead, two of tin, 
and one and a half of cadmium. The ingredients should 
be thoroughly mixed in each case. The melted alloy should 
be poured upon a slab of stone, its surface skimmed by 
means of a card ; and the medal or coin to be copied 



Moulding Objects. 225 

dropped upon it. As soon as the alloy has solidified, the 
coin may be removed ; the end of a clean copper wire at- 
tached to the mould by means of heat, the back of the alloy 
varnished, and the copy hung in the solution of sulphate of 
copper to receive the deposit. 

To copy a medal in wax, the medal (slightly oiled) 
should be surrounded by a rim of stiff paper about one 
inch deep, fastened by means of sealing-wax; then made 
quite warm, and the white wax in a melted state (but not 
too hot), poured upon it. When the wax has become solid, 
put it in a cold place for several hours, and then separate 
the coin and its copy ; but if the medal be a large one, the 
cooling process must be gradual, otherwise the wax may split. 

A good composition for copying coins, consists of 
two parts of gutta-percha, and one of Jeffery's marine 
glue. The two substances are cut up very small, heated 
very gradually, with constant stirring, until most tho- 
roughly mixed. To copy both sides of a medal in this 
mixture, take a strip of thin sheet copper, brass, or tinned 
iron, about an inch wide, wind it closely round the edge of 
the medal, and solder its ends together ; wipe the medal, 
and take two balls of the composition, quite hot and soft, 
and press them simultaneously against the two faces of the 
medal, working the material from the centre towards the 
circumference, to exclude bubbles of air ; place two thick 
plates of cold metal, one on each side, and gradually screw 
up the whole in a vice or press, gently at first, but in- 
creasing the pressure to a high degree as the materials be- 
come hard. When it is quite cold, which will be in about 
two hours, the two copies may be easily removed from the 
original, by inserting the ends of gimlets in their backs and 
drawing them out ; they are easily removed, because the 
composition slightly contracts in cooling. They will present 
fine impressions of the original, and be perfectly free from 
air-bubbles, if the operation has been carefully performed. 
A slight disadvantage attending the use of gutta-percha 

Q 



225 The A rt of Electro-Metallurgy. 

(and mixtures containing it) is, that it shrinks a little, in 
course ot a long period, but unless the surface is a large one, 
this defect is too small to be perceived 

All these mixtures require, of course, to have suitable 
conducting wires attached to them, and their surfaces black- 
leaded, or otherwise prepared, to render them conductive ; 
and those parts to which the conducting material has acci- 
dentally adhered, and which are not to be coated, must be 
1 stopped off' by means of a suitable varnish. Quick-drying 
spirit varnish is very suitable for the purpose, especially if 
some superfine red sealing-wax is dissolved in it, to render the 
coating more visible. It must also not be forgotten, that in 
all cases, the copy taken of an original object is not a fac- 
simile of the object, but its reverse, and that to obtain a 
fac-simile we must take a copy of the copy. For instance, if 
we take a mould of a coin in copper, either by means of elec- 
trolysis or in any other way, we must take a copy from this 
mould in order to obtain a real fac-simile. 

Copies of coins may also be taken in plaster of Paris. 
To copy a coin or medal in plaster it should be slightly 
oiled, and surrounded by a paper rim one inch in depth. 
Take the finest and freshest plaster (which has been kept in 
a well-closed bottle), mix it with water in a lipped vessel, to 
the consistency of treacle, then without delay brush a little 
of it over the surface of the coin with a camel-hair brush, 
and at once pour on the remainder. The plaster quickly 
sets to a solid state, and soon afterwards may be removed 
from the medal. The mould may be either itself copied 
in wax, etc., or be thoroughly dried, and then saturated with 
wax or tallow, by standing whilst still .hot in a shallow layer 
of the melted substance, until the latter has spread through- 
out its mass, and then at once remove it, and prepare its sur- 
face for receiving a deposit. Or it may be prepared for black- 
leading by saturating it with skimmed milk, and then drying it. 

Copying Buds, Statuettes, Statues, ere. — There are, how- 
ever, many objects which cannot be copied by any fo the 



Copying Busts, Statues, &c. 227 

methods above described, such as medals which are 'under- 
cut'; busts, statues, and figures of various kinds, because 
the mould formed upon the object cannot be removed with- 
out breaking either the original or its copy. In such cases 
either the mould or its copy, or both, are formed in pieces, 
so arranged that each piece may be removed ; or the copy 
of the object is taken in an elastic moulding material, which 
by allowing itself to be stretched, may be removed from 
overhanging, projecting, and undercut parts of the object, 
and then returns to its original form and dimensions. The 
best substance of this kind, and almost the only one used, is 
composed of four parts of the best thin glue and one of 
treacle ; the glue is broken into small pieces, and soaked 
several hours, or until it is quite soft, in sufficient cold 
water to cover it. The superfluous water is then thrown 
away, and the gelatine together with the treacle, is heated in 
a glue-pot (i.e. by immersing the vessel in boiling water), to 
nearly ioo° C, and stirred until the two substances are 
thoroughly mixed. The use of the treacle is to prevent the 
mould drying and shrinking. Some operators add half an 
ounce of beeswax for each pound of glue. 

The great disadvantage of such moulds is their ten- 
dency to absorb water, to swell, and to be partly dissolved in 
the solution of sulphate of copper. These difficulties are over- 
come, by using a depositing liquid containing the minimum 
proportion of water, and covering the mould as quickly as 
possible with the metallic deposit, any portions of it not 
requiring a deposit being previously well coated with a 
quickly- drying varnish, best, a solution of india-rubber in 
bisulphide of carbon. Various attempts have been made to 
enable the gelatine to resist more perfectly the action of the 
water, one of the most effectual of which is to dissolve in 
the mixture, two parts of tannic acid for each 100 parts of 
the dry glue, or to immerse the mould a few seconds in a 
solution of ninety parts water and ten of bichromate of 
potassium, and then expose it to the sun. 

Q 2 



228 The A rt of Electro- Metallurgy. 

If the object to be copied is a medallion with undercut 
parts, it is treated thus : — First well oil the medallion ; then 
encircle its edge by a strip of stout paper, and pour the 
mixture (quite hot, and of the consistency of treacle), upon 
its surface, to the depth of half an inch or more, according 
to the size of the medal, and the depth of its hollow parts, 
brushing its surface beneath the liquid with a brush having 
fine and long hairs, to remove air-bubbles. Allow the mix- 
ture to remain until it is quite firm, which will be from two 
to twenty- four hours, according to its bulk ; take off the 
paper, and remove the mould very gently, carefully stretch- 
ing and drawing it at the same time in the direction of the 
overhanging parts, to prevent injury. 

Should the object to be copied be a hollow metallic bust, 
proceed as follows :— First oil it, then partly fill it with sand, 
to make it heavy, and thus prevent its rising in the liquid, 
and cover its opening by fixing a piece of millboard strongly 
over it ; then place the bust in the centre of a circular and 
taper vessel, a few inches deeper and wider than itself, and 
pour the melted composition in steadily, until it is a few 
inches above the top of the head, tapping the bust, and in- 
clining the outer vessel, to facilitate the escape of air-bubbles. 
The composition will become firm in about twenty hours, 
and may be easily removed from the vessel by shaking, 
if the latter has been previously well oiled ; the mould may 
then be extracted from the bust, by previously marking on its 
lower end the position of the face, passing a knife carefully 
up the back of the bust nearly to the crown of the head, 
and opening the elastic mould with the hands whilst a second 
person lifts out the bust. If the original bust is composed 
of plaster, it must be previously saturated with oil, to prevent 
the melted composition adhering to it. In all cases, after 
fixing the necessary conducting and guiding wires to an 
elastic mould, it is rendered conducting by means of the 
silver or gold solutions, reduced to metal by means of phos- 
phorus or hydrogen, &c. 



Electro-Deposited Statues. 229 

Notwithstanding the greatest possible care having been 
taken in making and copying an elastic mould, failures are 
not infrequent ; either the coating of deposited metal is 
imperfect in the inmost parts of the mould, or the latter 
swells so greatly as to alter the figure of the object. Some 
objects are first copied in elastic composition, then the elastic 
mould re-copied in the phosphorus and wax mixture at the 
lowest possible temperature, so as not to melt the gelatine ; 
the mould removed, and the other deposited upon. 

Bubbles of air often adhere to moulds immersed in de- 
positing solutions ; they may be prevented by previously 
dipping the object in spirit of wine; or be removed by the aid 
of a soft brush, or by directing a powerful upward current of 
the liquid against them by means of a vulcanized india-rubber 
bladder, with a long and curved glass tube attached to it ; 
but the liquid should be free from sediment. 

With large objects, such as statues, a different plan from 
any of those already described is resorted to ; in this case, 
instead of employing elastic moulds, the copy itself is sacri- 
ficed. The original figure, formed of plaster of Paris, and 
obtained from a modeller or sculptor, is saturated all over 
its surface with boiled linseed oil. It is then coated with 
extreme care in all parts with a shining film of black-lead, 
by prolonged brushing, or with a film of silver by means of 
the phosphorus and silver solutions ; but the presence of 
phosphorus is apt to make the deposited copper brittle. It 
is then immersed in a large cistern of the sulphate of copper 
solution (see p. 206), and coated entirely with copper to a 
thickness of about ^th of an inch, or sufficiently to retain its 
form when the inner figure is removed. It is now lifted 
out of the vat, washed, the copper cut through at suitable 
places, the plaster figure broken away with great care, 
and the whole of it extracted. The outer surfaces of the 
copper forms, (with wires attached) are now thoroughly 
varnished all over, to prevent any deposit being formed 
thereon ; the forms exposed to sulphuretted hydrogen, 1 1 



230 The A rt of Electro-Metallurgy. 

dipped into a weak solution of sulphide of potassium, to 
prevent adhesion of the deposit ; the parts immersed in the 
depositing vat again, and filled with copper solution. A dis- 
solving plate of pure electrotype copper is suspended within 
each portion, and a deposit of copper thus formed all over its 
interior, until a considerable thickness, varying from \ to \ of 
an inch, is deposited, which requires a period of three or four 
weeks. Each piece is now removed from the liquid, washed, 
and the outer shell torn off, when all the parts of the figure 
remain nearly complete and ready for fixing together. Some 
of the objects made by this process by Messrs. Elkington are 
colossal ; that of the Earl of Eglinton is 13 \ feet high, and 
weighs two tons ; and the vat in which it was formed, is 
15 feet long, 9 feet deep, and 8 feet wide, and is capable of 
containing 6,680 gallons of liquid. Messrs Christople of Paris, 
made a statue of 9 metres (=29 feet 6 in.) high, weighing 
3,500 kilogrammes (=atout3 tons 9 cwt), and of a thick- 
ness of \\ millimetres. It occupied about ten weeks in 
depositing. As it is difficult in practice to deposit the figures 
of a man, horse, &c. all in one piece, this plan of dividing the 
first copper figure in suitable parts, usually at the lower edge 
of the vest, the shoulders and wrists, and depositing upon 
the interiors of these, and fastening the separate deposits to- 
gether to form the complete figure, is nearly always adopted. 
Lenoir employs a different process, which may be briefly 
stated as follows : — An external copy of the figure is made 
of gutta-percha in several parts, so as to be capable of being 
put together and form the complete figure; and the internal 
surfaces of these pieces are black-leaded. An outline figure 
of the object, but of somewhat smaller dimensions, is formed 
of platinum wire, to act as an anode, and the pieces of gutta- 
percha are fixed together to form the complete figure around 
it. The mould is placed in a vertical position, the platinum 
outline figure being suspended in it by means of its connecting 
wires, and prevented from touching the mould by partly 
covering the wire with a spiral of india-rubber thread. The 



Etching Copper Plates. 231 

mould and its anode (previously weighted) are now immersed 
in the same vertical position in the copper solution, the 
battery connected, and a current of the liquid caused to con- 
tinually enter the mould by a hole at the top of the head 
and escape by two holes at the feet After a sufficient 
deposit is formed, the flexible anode of wire is drawn out 
through the hole in the head, the parts of the gutta-percha 
mould are taken asunder, and the seams in the copper at 
the junctions of the model are then removed by filing, &c. l 

Glyphography. — The process of glyphography consists 
in coating a plate of copper with two thin layers of en- 
graver's wax composition, the first one white, and the second 
black, engraving the design through the wax to the copper 
beneath, then black-leading the entire surface of the wax, 
varnishing the back of the copper plate, and depositing copper 
upon the entire front surface until a stout plate of metal is 
formed. The plate is then removed, strengthened with solder, 
mounted like a stereotype plate, and employed for printing 
in the usual manner. Before black-leading, it is sometimes 
necessary to thicken the wax coating over large white spaces, 
the middle portions of which might otherwise print black. 

Etching copper plates. — In etching a copper plate by 
galvanism, we first solder a wire to it, then varnish the 
back, and cover the front with a thin layer of engraver's 
etching-ground ; draw the design upon the front surface 
with an etching needle, cutting through this material to the 
clean surface of the copper. Having completed the etching, 
hang the plate as an anode in the ordinary sulphate of 
copper solution, opposite a suitable cathode of copper. 
The current of electricity in passing out of the engraved 
lines into the liquid, causes the copper in them to dissolve, 
and thus etches the design on the plate. The various 
gradations of light and shade are produced by suspending 
cathodes of different forms and sizes opposite the plate to 

1 M. Plante employs, instead of the platinum wire outline, a thin 
hollow anode of lead pierced with holes. 



232 The A rt of Electro- Metallurgy. 

be etched, in varied positions, and at different distances from 
it, thus causing the plate to be corroded to unequal depths 
in different parts, the deepest action being always at those 
portions of the electrodes which are nearest together. 

Depositing copper upon glass, &-r. — The only effectual 
way of obtaining an adhesive deposit upon glass or por- 
celain, is to send the article to a glass and porcelain gilder, 
and have gold burnt into its surface, and then depositing 
upon the gold coating in the usual manner. 

16. Nickel. — Elec. chem. eqt.= — = 29*5. The com- 
monest salts of nickel, are the oxide, nitrate, chloride, car- 
bonate, and sulphate. The oxide is a black powder, 
soluble in nitric, hydrochloric, and sulphuric acids ; the 
nitrate and chloride are green salts freely soluble in water ; 
the carbonate is a pale green powder readily soluble in most 
acids ; the sulphate is a freely soluble salt. The oxide may 
be made by heating the carbonate or nitrate to redness, or 
by precipitating a solution of a salt of nickel with caustic 
potash or soda. The nitrate may be made by digesting 
the metal, its oxide or carbonate, in dilute nitric acid, and 
evaporating the solution ; the chloride may be formed with 
hydrochloric acid in a similar manner, or by adding an 
excess of that acid to a solution of the nitrate, and evaporat- 
ing the mixture to dryness. The carbonate may be formed 
by adding a solution of carbonate of sodium to one of any 
salt of nickel, and washing and drying the precipitate. The 
sulphate may be made by digesting either the oxide, nitrate, 
chloride, or carbonate in an excess of dilute sulphuric acid, 
and evaporating the solution nearly to dryness. A solution 
of the nitrate, chloride, or sulphate, may also be obtained by 
making a bar of nickel (or fragments of nickel, suspended 
on platinum wire gauze) the anode in dilute nitric, hydro- 
chloric, or sulphuric acid, and passing the current until the 
acid is sufficiently saturated with metal. 

Electrolysis of salts of nickel. — I have electrolysed dilute 



Electrolysis of Salts of Nickel. 233 

hydrochloric acid by means of one Smee's element, an anode 
of nickel and a cathode of copper. The conduction was very 
feeble, and a film of iron grey metal was deposited upon the 
cathode in twelve hours. A dilute solution of nitrate of 
nickel did not yield its metal freely. By making a strong 
solution of salammoniac, or of sulphate of ammonium, and 
passing a strong current through it, by means of an anode of 
nickel during several hours, until the liquid acquired a pale 
greenish blue colour, I obtained a deposit of coherent white 
metal. A good solution for depositing nickel, is the double 
cyanide of nickel and potassium, to which some common 
salt has been added. 

Nickel has also been deposited from a liquid formed by 
precipitating a solution of nitrate of nickel with carbonate 
or cyanide of potassium, washing the precipitate and dis- 
solving it nearly to saturation in a solution of potassic 
cyanide, and operating upon the liquid by the battery 
process with an anode of nickel. The metal deposited from 
this solution is said to be nearly equal in whiteness to silver. 
According to Smee, a solution of chloride of nickel is an 
excellent one for deposition, because of its small tendency 
to evolve hydrogen at the cathode. The nickel deposited 
from it ' has a peculiar white brilliant lustre, looking almost 
like glass ; this deposit is so very beautiful, though brittle 
when removed from the negative pole, that its examination 
would amply repay any person taking the trouble to precipi- 
tate it.' He also states that a solution of the acetate yields 
a black powder deposit, and is a bad one for obtaining 
reguline metal. 

Merrick has electrolysed a number of solutions of salts 
of nickel by means of a current from two Grove's cells, an 
anode of nickel and a cathode of platinum, placing a volta- 
meter for mixed gases in the circuit to measure the strength 
of the current, and a rheostat to keep the current uniform. 
He weighed the metallic deposits. The nitrate yielded a 
thick greenish non-metallic deposit (probably a basic 



234 The A rt of Electro-Metallurgy. 

nitrate), with a metallic layer beneath. A solution of sp. gr. 
1*0503 of the pure chloride, yielded an adherent deposit of ' 
metal with a non-adherent layer of black powder upon it. 
The quantity of metal obtained equalled 83*6 per cent of 
the theoretical amount. With a solution of commercial sul- p 
phate of nickel, there was a great evolution of gas from the 
cathode, and much from the anode; and two layers of 
deposit, the outer one greenish and non-adherent, the lower 
one speckled and blotched metal. A solution of sp. gr. 
1 "0223 of the pure sulphate, gave a blackish deposit of I 
metal, equalling 52 per cent of the theoretical amount, | 
streaked with a non-adherent greenish deposit of subsul- f 
phate above it. With a solution of sp. gr. 1-0232 of the H 
acetate, much of the deposit was black oxide in powder. 
The coherent metallic layer beneath, equalled 10 per cent 
of the theoretical amount. A solution of the cyanide of 
nickel and potassium, evolved much gas at the cathode, 
and gave a dull blackish-grey metallic deposit equal to 14 
per cent of the theoretical quantity. One of the ammonio- 
nitrate, of sp. gr. roi6, yielded a variously coloured 
metallic deposit amounting to 97*4 per cent of the theore- 
tical amount, beneath a layer of greenish subsalt. The 
double chloride of nickel and ammonium, gave a pulverulent 
deposit, with a metallic one beneath, equal to 47 per cent | 
of the theoretical quantity. The ammonio-chloride yielded 
96 per cent of the required quantity of metal, partly bright, 
and partly dull. The double sulphate of nickel and 
ammonium, gave a good metallic deposit, equalling 93-5 per 
cent of the theoretical amount. The ammonio-sulphate 
gave 96 per cent in the form of greyish-brown metal; the 
solution was formed by adding an excess of ammonia, and 
then alcohol, to a strong solution of nickel sulphate, and 
dissolving the precipitated salt in water. A solution of the 
pure sulphate of nickel and potassium, evolved much gas 
from the cathode, and gave a blackish-green deposit, with a 
dull metallic layer beneath. The layer of metal contained 



Nickel- F Hating by Simple Immersion Process. 235 

j 37 per cent of the theoretical amount of nickel. (* Chem. 
\ News/ vol. xxvi. p. 209 ; also ' Journal of the Chemical 
i Society,' vol. xi. p. 204.) A solution of hydrated oxide of 
'! nickel, in a mixture of cream of tartar, and a little soda and 
j water, electrolysed by means of a current from two Daniell's 
! cells and platinum electrodes, yields a layer of solid hydrated 
\ peroxide of nickel upon the anode (W. Wernicke, ' Journal 
!; of the Chemical Society,' vol. ix. p. 307). 

Deposition of nickel by simple immersion. — Nickel is not 
i usually deposited by simple immersion process in aqueous 
! solutions ; it is too electro-positive. Crystalline silicon 
j separates nickel from its anhydrous fluoride by the assist- 
! ance of heat. I mixed 1*5 grain of crystals of silicon 
with ten of dry fluoride of nickel, and heated the mixture. 
At a gentle red heat in a porcelain crucible, vivid incan- 
descence occurred, and metallic nickel was deposited and 
melted by the evolved heat. The globules were grey, 
looked like nickel, and were feebly attracted by a magnet, 
I also immersed crystals of silicon in an aqueous solution 
of fluoride of nickel containing free hydrofluoric acid ; the 
crystals did not coat themselves with metal. According to 
I. C. Davies, nickel is scarcely precipitated at all from acid 
solutions by means of zinc; but if ammonia be added to the 
liquids, precipitation occurs. Zinc throws down the metal 
perfectly from a solution of nickel chloride rendered ammo- 
niacal. A. Merry obtained similar results with sulphate 
solutions ('Journal of the Chemical Society,' vol. xiii. p. 311). 
' According to M. Becquerel, the simple immersion of copper 
in a solution of the double chloride of nickel and sodium, 
is sufficient to deposit the metal ('The Chemist,' vol. v. p. 
408). Magnesium deposits hydrated protoxide of nickel 
from a solution of nickel sulphate (Commaille, ' Chemical 
News,' vol. xiv. p. 188). But from slightly acid solutions of 
salts of protoxide of nickel, magnesium deposits hydrogen 
and metallic nickel (Roussin, ' Chemical News,' vol. xiv. 
p. 27). 



236 The A rt of Electro-Metallurgy. 

Depositing ?iickel by contact with another metal (see also v 
p. 82). — C. Mene coats articles of iron, steel, copper, brass, II 
zinc, and lead, by immersing them in contact with zinc, in : 
a boiling neutral solution of chloride of zinc, containing 
metallic nickel in fragments or plate. If the solution is acid,; 
the coating will be dull (' Chemical News,' vol. xxv. p. 214).^ 
Stolba adds two measures of water to one of concentrated] 
solution of chloride of zinc in a copper vessel, boils the! 
mixture, and re- dissolves any precipitate by the least possible 1 
quantity (a few drops) of hydrochloric acid. A few particles \ 
of powdered zinc are thrown into the liquid ; and this causes \ 
a deposit of zinc upon the vessel. Sufficient chloride or sul- 
phate of nickel is then added until the liquid is distinctly 
green ; and the previously cleaned articles are at once \ 
immersed in contact with zinc in the boiling liquid during 
fifteen minutes. For thick coatings the operation is repeated. \ 
Articles of zinc, cast iron, wrought iron, steel, brass, and = 
copper, are coated by this process. According to Raoult, 
gold in contact with nickel, either in a cold or boiling, acid 
or neutral, solution of salts of nickel, receives no metallic 
deposit ('Journal of the Chemical Society,' vol. xi. p. 465). [ 

Depositing nickel by separate current process (see alsoi ; 
p. 89). — Nickel is not usually deposited by the single cell f 
method, because that process robs the liquid of metal, I 
and sets free its acid, and an acid solution of nickel is ! 
difficult to manage. Various solutions have been tried for } 
practical use by the separate current method, but the most ! 
successful ones have been those composed of the double I 
salts of nickel and ammonium. In the year 1855 I employed ! 
the double salts of nickel and ammonium for depositing the ■• 
metal, and published the results of the use of them. In 
August 1869 Dr. Isaac Adams patented those salts for nickel I 
plating purposes, and nearly all the deposition of nickel has I 
been done by their aid. The liquids contain various pro- 
portions of the salts to the water, but are usually strong. 

The credit of depositing nickel upon a large scale, and 



Nickel- Plating Solutions. 237 

coating other metals extensively with it, has been given to 
Dr. Adams (see 'Chemical News/ vol. xxi. p. 69). According 
to the terms of his patent he claims that the solution must 
be free from potash, soda, lime, alumina, and nitric acid ; 
according also to M. GaifTe it should not contain a trace of 
salt of potash or soda ; but Becquerel disproves this, and 
shows that the double sulphates of potassium and nickel, 
may be used with equal success to those of ammonium and 
nickel ; and that the bath must not be allowed to become 
acid (' Chemical News/ vol. xxi. p. 57). H. Bouillet also 
denies the necessity of absence of the fixed alkalies in 
depositing nickel, and says : ' I have deposited good nickel 
from the double sulphate of nickel and magnesium' 
('Chemical News/ vol. xxii. p. 22). 

Becquerel employed a solution of sulphate of nickel, with 
its free acid neutralized by ammonia, and kept the sulphuric 
acid which was liberated by the electrolysis, saturated with 
metal by means of oxide of nickel placed in the liquid, or 
neutralized it by occasionally adding ammonia. When the 
oxide is employed for replenishing, the liquid remains of the 
same degree of concentration ; but with ammonia, it depo- 
sits clear green crystals of double sulphate of nickel and 
ammonium ; these are very slightly soluble in water alone, 
but more freely in that containing ammonia. The de- 
posited nickel is brilliantly white, and may be formed into 
bars, &c, by electrolysis, by having proper moulds to receive 
it ; the bars possess magnetic polarity. The solution of 
double sulphate of nickel and ammonium, whether containing 
free ammonia or not, yields metal by electrolysis (Becquerel, 
' Chemical News/ vol. vi. p. 126). 

Bottger states that he has tried many nickel solutions, but 
the best was made by adding to dry crystals of protosulphate 
of nickel, as much liquid ammonia as was necessary to dis- 
solve them. The dark blue fluid was then ready to use by 
the battery process (' Pharmaceutical Journal/ vol. iii. 
P- 358). 



238 The A rt of Electro-Metallurgy. 

M. Nagel adds one part of aqueous ammonia to thirty 
parts of water, then dissolves in it two parts of crystals of 
sulphate of nickel, and adds six parts of aqueous ammonia 
of sp. gr. '909. He uses the solution at a temperature of 
about ioo° Fahr. with a platinum anode, and a moderate 
current. 

Another solution is formed as follows: — Take 150 parts 
of water, add twelve and a half of nitric acid, five of chloride 
or sulphate of ammonium, five of nitrate of ammonium, 
heat the mixture to 80 C, and saturate it with freshly pre- 
cipitated hydrate of nickel, made by precipitating a solution 
of chloride or sulphate of nickel, by one of caustic potash 
or soda; cool the mixture, add twenty-five parts of aqueous 
ammonia, dilute the whole with water to 250 parts, dissolve 
in it five parts of carbonate of ammonium, filter the liquid 
and use it at a temperature of 50 C. (' Chemical Society's 
Journal,' vol. xii. p. 928). 

Another solution is composed of 100 parts of sulphate 
of nickel, fifty-three of tartaric acid (dissolved in water), 
and fourteen of caustic potash added: it is said to yield a 
deposit of very great beauty, having a bright silver lustre, 
without scratch-brushing. 

According to Roseleur, nickel may be deposited as a dull 
grey metal, from a solution made by dissolving nitrate of 
nickel in its own weight of aqueous ammonia, and diluting 
the mixture with twenty or thirty times its volume of aqueous 
bisulphite of soda solution of sp. gr. 1*199. 

Thomas and Tilley. according to their patent of Dec. 26, 
1854, precipitate a solution of chloride of nickel with ferro- 
cyanide of potassium, and dissolve the washed precipitate 
in a solution of cyanide of potassium, to form a depositing 
liquid. 

Management of nickel plating solutions. — The solutions 
are generally contained in vats of wood, lined with asphal- 
tum (see p. 313). As metallic nickel is much like cast iron, 
and cannot be rolled, the anodes are composed of plates of 



Management of Nickel- Plating Solutions. 239 

the cast metal, usually about 12 inches deep, 9 inches wide, 
and half an inch or more in thickness ; and should have 
a much larger surface facing the articles, than that of the 
articles themselves. Cast nickel contains a variable propor- 
tion of copper, carbon, and silicon ; and when it dissolves, 
the carbon and silicon are thrown out upon the surface in 
the form of a black powder, which falls to the bottom ; the 
copper dissolves and is deposited. If plates of nickel can- 
not be obtained, fragments of metallic nickel should be sus- 
pended in baskets of platinum-wire gauze, but this is not a 
very practical plan, because the current becomes impeded 
by the impurities ; or a quantity of freshly precipitated 
hydrated oxide of nickel in a wet state should be added to 
the solution, and the liquid stirred up each evening. 

Nickel solutions are less easy to manage than those of 
silver. Some of those employed, contain a large quantity 
of the double salt, others contain about four ounces per 
gallon. The chief point to be attended to, is to keep the 
solution neutral or slightly alkaline; a few operators, how- 
ever, prefer a slight degree of acidity. They should be 
frequently tested with neutral tint litmus-paper ; and am- 
monia should be added if necessary. It is also desirable 
to employ a much larger surface of anode than that of 
the articles, and to keep the anodes in the liquid whilst 
the current is not passing ; by these means liberation of 
much free acid is avoided. The current should also be 
maintained very uniform, and the articles kept in motion. 
During the electrolysis, more or less hydrogen is usually 
evolved at the cathode, but this of course depends upon the 
composition of the solution, and the ' density' of the current ; 
in consequence of this, it is difficult to obtain thick deposits, 
the hydrogen is set free in the metal, and causes it to split 
off in films. The articles to be coated should be very clean, 
and also free from scratches ; the latter cause an irregular 
deposit. A current from one to three cells of large surface 
is usually sufficient. 



240 The Art of Electro- Metallurgy. 

Properties, uses, &°c, of electro-deposited nickel. — Electro- 
deposited nickel is hard, too hard to be burnished, and 
therefore resists rough usage, and is very much more durable 
than an equal thickness of silver, but the deposits are usually 
very thin. ' Laminae of electro-deposited nickel sometimes 
contain forty times their volume of hydrogen '(MM. L. Troost 
and P. Hautefeuille (' Chemical News,' vol. xxxi. p. 196). 

Nickel has sometimes a dull appearance when deposited, 
but in consequence of its hardness a high degree of polish 
may be imparted to it by mechanical means. It must not 
be 'scratch-brushed' with brass brushes, because they 
make it yellow. Its colour when polished, is more blue 
than that of silver, and changes to a slightly yellowish 
tint by lapse of time. It does not readily oxidise in the air, 
even when wet ; but it is easily corroded by acids. Whilst 
silver is rapidly blackened by sulphuretted hydrogen, nickel 
is not affected. In consequence of its hardness, and in- 
difference to sulphuretted gases, it retains its polish a very 
long time. Nickel should not be employed for coating the 
interior of cooking utensils, because of its being corroded by 
acids, and having poisonous properties. Although metallic 
nickel is much less expensive than silver, the cost of nickel- 
plating is not proportionately less, because the value of the 
metal is not the greatest part of the expense. In America, 
spoons and forks are said to be coated at twenty-five cents 
per dozen, and saddlery trimmings at thirty cents. It is 
very useful for harness furniture, carriage fittings, scales and 
weights, points of lightning conductors, and for many other 
purposes, and the electro-deposition of it has greatly ex- 
tended. There are establishments in which it is carried on, 
in Birmingham, Sheffield, London, New York, Philadephia, 
and other places ; at the Star Nickel-plating works, Phila- 
delphia, they operate in accordance with the patents of 
Dr. Isaac Adams. 

Estimation of ?iickel by means of the battery. — A solution 
containing one gramme of the pure double sulphate of nickel 



Salts of Cobalt. 24 1 

and ammonium was analysed; with a current from two 
Grove's cells, it required two hours for its reduction, and 
yielded in three experiments 1479, I 47 8 ; an d 1477 per 
cent of nickel ; the theoretical amount is 1472 per cent. 
Samples of the commercial sulphate, gave 22-07, 2l '%7, 21*84, 
21*43, and 22*05 per cent ; theory required 20*71 per cent. 
The double sulphate of nickel and potassium gave 13*33, 
13*37, and 13*24 per cent; theory required 13*29 per cent. 
With a larger amount of the same salt, 13*24 per cent was ob- 
tained. The double phosphate of nickel and potassium, 
yielded 13*27 per cent, theory requiring 13*29. The 
metallic deposits were washed with alcohol, and cautiously 
dried (I. M. Merrick, ' Chemical News,' vol. xxiv. pp. 100, 
172). 

17. Cobalt. — Elec. chem. eqt. = ^ = 29*6. Metallic 

cobalt, especially in the form of bars or plates, can rarely be 
obtained, because it is not only extremely difficult to melt, 
but there is very great loss by oxidation in the process. The 
commonest salts of cobalt, are the oxide, nitrate, and chloride. 
The oxide may best be purchased : there are two varieties 
of it, one a black powder containing more oxygen, and the 
other brownish black, and containing less, having been more 
strongly heated. The chloride may be made, by digesting 
the oxide in hot and strong hydrochloric acid, and evapo- 
rating the deep blue liquid ; it yields purplish red crystals, 
freely soluble in water. The nitrate is prepared by digest- 
ing the oxide in nitric acid, and evaporating the solution ; 
it is in the form of deliquescent red crystals \ freely soluble 
in water. 

According to Becquerel, copper immersed in a solution 
of double chloride of cobalt and sodium, acquires a coating of 
cobalt (' The Chemist,' vol. v. p. 408). Magnesium slowly 
deposits hydrated oxide of cobalt from a solution of the 
sulphate (Commaille, 'Chemical News,' vol. xiv. p. 188). 
But from slightly acid solutions of protoxide of cobalt, mag- 

R 



242 The A rt of Electro-Metallurgy. 

nesium deposits metallic cobalt and hydrogen gas (Roussin, 
'Chemical News,' vol. xiv. p. 27). 

Electrolysis of salts of cobalt. — Very little has been done 
to ascertain the behaviour of these salts by electrolysis. 
I electrolysed the fluoride dissolved in pure dilute hydro- 
fluoric acid, with a current from a single Smee's element, 
an anode of cobalt, and a cathode of copper. The con- 
duction was very sparing, and only a film of black powder 
appeared on the cathode in twelve hours. According to j 
Smee, this metal may be reduced from its chloride (to which ' 
an excess of ammonia has been added) by using a cobalt ' 
anode, a series of battery cells, and a cathode of copper, i 
The reduced metal is white, but is not deposited freely. 1 
It may also be reduced from a solution, formed by digesting 
oxide of cobalt in cyanide of potassium j but only in small 
quantity, hydrogen being freely evolved. 

W. Wernicke says that the hydrated oxide, dissolved in 
water containing cream of tartar and a little caustic soda, 
yields, when electrolysed with electrodes of platinum, solid 
hydrated peroxide of cobalt upon the anode. The deposit 
exhibits magnificent interference colours, which are valuable 1 
for the purposes of metallo-chromy, and are readily produced, ' 
and permanent (' Chemical News/ vol. xxii. p. 240 ; ' Journal j 
of the Chemical Society,' vol. ix. p. 307). 

Deposition of cobalt by contact with another metal. — C. 
Mene deposits the metal upon articles of zinc, lead, iron, j 
brass, or copper, by immersing them in contact with zinc, ' 
in a boiling hot and neutral solution of chloride of zinc, 
containing fragments of metallic cobalt (' Chemical News,' ! 
vol. xxv. p. 214). According to Stolba, salts of cobalt treated ' 
in a similar manner to those of nickel (see p. 234), yield a 
metallic deposit of a steel-grey colour, less lustrous than nickel, 
and more liable to tarnish. 

Deposition of cobalt by separate current process. — Accord- ; 
Ing to Becquerel, a concentrated solution of the chloride, 
with its excess of acid neutralised by addition of caustic j 



Deposition of Cobalt by Separate Current. 243 

potash or ammonia, and electrolysed by a very weak current, 
deposits its metal in coherent tubercles, or in uniform 
layers, according to the strength of the current. The de- 
posited metal is brilliantly white, hard, and brittle, and may 
be obtained in cylinders, bars, and medals, by using proper 
moulds to receive it. The deposited rods are magnetic, and 
possess polarity. With an anode of cobalt, it is unnecessary 
to alter the solution after its first preparation. Part of the 
chlorine of the solution is disengaged during the electrolysis. 
If the liquid contains iron, the greater portion of it is not 
deposited with cobalt (' Chemical News/ vol. vi. p. 126). 

To deposit the metal, dissolve five ounces of the dry 
chloride in a gallon of distilled water, and make the solution 
slightly alkaline with ammonia. Pass the current through 
the liquid, either by using a plate of cobalt as anode, or a 
bar of gas-carbon in contact with a heap of fragments of 
cobalt contained in a gutta-percha basket. From two to 
five Smee's cells are required. The solution must be kept 
slightly alkaline ('Telegraphic Journal/ vol. ii., p. 246). 
'Laminae of electro-deposited cobalt, sometimes contain 
thirty-five times their volume of hydrogen ' (Troost and 
Hautefeuille, ' Chemical News/ vol. 31, p. 196). 

18. Iron. — Elec.-chem. eqt. = 5— = 28. A plate of 

2 

iron 15 centimetres square, and two millimetres thick, was 
deposited on copper by Herr Bockbushmann, in the year 
1846. In 1857, M. Feuquieres exhibited specimens of 
electro-deposited iron at the Paris Exhibition. In 1858, 
M. Gamier patented his process, termed acierage (steeling), 
for protecting the surfaces of engraved copper plates j and 
in the same year, Klein produced his beautiful specimens of 
electro-deposited iron. 

Iron is a very impure metal, and liable to contain carbon, 
silicon, &c. ; its least impure form is wrought iron. Its 
commonest salts are the peroxide, (called also sesqui-oxide 
of iron, jewellers' rouge, &c); the protosulphate, (called 



244 The Art of Electro-Metallurgy. 

also green vitriol) ; the carbonate ; the protochloride ; and 
the perchloride. The peroxide may be readily obtained, 
by adding some nitric acid to a solution of green vitriol, 
boiling the mixture, adding an excess of aqueous ammonia, 
and washing and drying the precipitate ; it is a brick-red 
powder. The protosulphate is most conveniently purchased, 
it is very cheap ; it may however be prepared, by digest- 
ing fine iron wire in partly diluted sulphuric acid, in a nearly 
filled and covered glass vessel, until no more will dissolve, 
and then evaporating the solution, as much as possible out 
of contact with air; it is a green crystalline salt, freely soluble 
in water. The protochloride may be similarly prepared, 
by using hydrochloric acid instead of sulphuric; it is also 
of a green colour, and very soluble. The solutions of all 
protosalts of iron, rapidly absorb oxygen from the atmo- 
sphere, and become persalts. The perchloride is made, by 
adding some nitric acid to a solution of the protochloride, 
and then boiling the mixture down to the crystallising point 
in a wide porcelain dish ; it is a brick-red salt, very soluble 
in water, and liable to produce a cloudy solution. 

Depositio?i of iron by simple im?)iersio?i (see p. 79). — Mag- 
nesium deposits from a neutral solution of ferrous sulphate, 
hydrated ferrous oxide, but from an acidified solution it 
deposits metallic iron (Commaille, ' Chemical News,' vol. 
xiv. p. 188). From slightly acid solutions of proto and 
sesqui salts of the metal, magnesium deposits pure iron and 
hydrogen gas (Roussin, 'Chemical News/ vol. xiv. p. 27). 
Gold in contact with iron, and immersed in cold or boiling, 
acid or neutral, solutions of salts of iron, does not receive 
a metallic deposit (Raoult, ' Chemical News/ vol. xxvi. 
p. 240, vol. xxvii, p. 59 ; 'Journal of Chemical Society/ vol. 
xi p. 465). 

Electrolysis of salts of iron. — Iron maybe reduced from a 
solution of its protosulphate (green copperas), or from its 
protochloride, which is preferable. I have deposited it in 
the state of reguline white metal, by passing a current of 



Electrolysis of Salts of Iron. 245 

considerable intensity (from fifteen or twenty Smee's cells), 
for one hour, through an anode of iron immersed in a satu- 
rated aqueous solution of salammoniac ; its appearance when 
deposited from this liquid is rather white, very similar to 
that of freshly broken cast iron. By similar means it may 
also be deposited, using a saturated solution, either of car- 
bonate of ammonium, acetate of ammonium, or acetate of 
potassium. Good metal may also be deposited from a satu- 
rated aqueous solution, of a mixture of two parts of protosul- 
phate of iron and one of salammoniac. I have deposited 
it from an aqueous solution of ferrate of potassium, formed, 
either by igniting peroxide of iron very strongly for some 
minutes with caustic potash and saltpetre, and dissolving 
the product in water ; or by making a very strong solution 
of caustic potash, immersing in it a large iron or steel anode, 
and a small copper or platinum cathode, and passing a strong 
current from fifteen or twenty Smee's cells through it, until 
it acquires a deep amethystine or purple colour ; by that 
time, the cathode will have obtained a coating of iron, which 
will be in the state of a dark powder if the power has been 
too great, or it will have the appearance of white cast iron 
(or intermediate between that and the appearance of reguline 
deposited zinc), if the power has been sufficiently weak. 
The solution rapidly decomposes, becomes colourless, and 
deposits all its metal in the state of peroxide at the bottom 
of the vessel. Iron may be very easily deposited from its 
sulphate thus : dissolve a little of the salt in water, and add 
a few drops of sulphuric acid to the solution ; one Smee's 
cell may be used to deposit it upon copper or brass. The 
metal inks pure coherent state, has a very bright and beauti- 
ful silvery appearance. An aqueous solution of cyanide of 
potassium is a very bad conductor with an iron anode, even 
if it be maintained hot. Solutions of persalts of iron yield 
no metallic deposit, but are reduced to protosalts, by the 
passage of an electric current through them. 

Walenn deposited reguline, white, silvery-looking iron, 



246 The A rt of Electro-Metallurgy. 

(attended by the evolution of much hydrogen) from a cold 
and slightly acid solution, composed of one part of crystal- 
lised ferrous sulphate, dissolved in five of water ; employing 
a current from three Smee's elements of about ten times the 
amount of surface as that of the electrodes. The addition 
of sulphate of ammonium increased the conducting power, 
and formed a very good depositing solution ('Chemical 
News/ vol. xvii. p. 170). 

One of the best liquids for depositing iron, is that of 
M. Klein, prepared as follows : — Precipitate a solution of 
ferrous sulphate (green vitriol) by means of carbonate of 
ammonium, and dissolve the washed precipitate in sul- 
phuric acid, taking care to avoid any free acid. Use the 
bath as concentrated as possible. Good reguline metal 
may be obtained from it, by means of a current from 
four weak Meidinger's cells, with an anode of iron and a 
cathode of copper. It is highly important to prevent the 
bath becoming acid by the working, &c, and this is effected 
by using an anode eight times the size of the receiving sur- 
faces, and by attaching a plate of copper or platinum to 
it, so that the two form a voltaic pair in the liquid, and 
thus cause the iron to dissolve whilst the battery current is 
not passing. The metal obtained from it, is as hard as tem- 
pered steel, and very brittle, but after annealing, it is malle- 
able, and may be engraved as easily as soft steel. He also 
employs a bath, composed of the double sulphate of iron 
and magnesium, of sp. gr. 1-155 > tne liquid must be neutral, 
and the electric current very feeble. The iron obtained 
from it has a sp. gr. of 8-139 ; it occludes thirteen times 
its volume of hydrogen, and possesses a higher electric con- 
ductivity than any commercial iron ; it does not warp or 
contract when heated, but slightly expands, and is not 
porous (' Chemical News,' vol. xviii. p. 133, and vol. xxxi. 
p. 137 ; 'Telegraphic Journal/ vol. ii. p. 128). 

' Copying engraved metal plates with copper and giving them 
a surf ace of iron. — If the engraved plate is of steel, boil it one 



Facing Copper Plates with Iron. 247 

hour in caustic potash solution . Brush and wash it well. Wipe 
it dry with a rag, and then with one moistened with benzine. 

'Melt six pounds of the best gutta-percha very slowly 
indeed, the gum being previously cut up into very small 
pieces. Add to it three pounds of refined lard, and 
thoroughly incorporate the mixture. Pour the melted sub- 
stance upon the centre of the plate. Allow it to stand twelve 
hours, and then take the copy off. 

' Phosphorus solution. — Dissolve a fragment of phosphorus 
half an inch in diameter, in one teaspoonful of bisulphide 
of carbon, add a similar measure of pure benzine, three drops 
of sulphuric ether, and half a pint of spirits of wine. Wash 
the mould twice with this solution, allowing it to dry each 
time. 

' Silver solution. — Dissolve one-sixth of an ounce of nitrate 
of silver, in a mixture of half a pint of strong alcohol, and 
half a teaspoonful of acetic acid, wash the mould once with 
this liquid, and allow it to dry. 

' Copper solutions. — Dissolve fifty-six pounds of sulphate 
of copper, in nineteen gallons of water, and add one gallon 
of oil of vitriol. Deposit a plate of copper upon the mould 
in this solution. 

* Iron solution. — To coat the copper plate with a surface 
of iron, dissolve fifty-six pounds of carbonate of ammo- 
nium, in thirty-five gallons of water. Dissolve iron into the 
liquid, by means of a clean anode of charcoal iron, and a 
current from a battery. Clean the anode frequently, and 
add one pound of carbonate of ammonium once a week. The 
copper plate before receiving the deposit, should be cleansed 
with pure benzine, then with caustic potash, and thoroughly 
with water. Immerse the cathode in the iron solution for 
four minutes, take it out, wash, scrub, re-place in the vat, 
remove and brush it every five minutes, until there is a suffi- 
cient deposit. Then wash it thoroughly, well dry, oil and rub 
it, and clean with benzine. If it is not to be used at once, 
coat it with a film of wax. 



248 The Art of Electro-Metallurgy. 

Meidinger coats engraved copper plates with iron, in a 
solution of sulphate of iron and chloride of ammonium ; 
and the plates serve for as many as from 5,000 to 15,000 
impressions (Wagner's 'Technology,' p. 116). 

Management of iron depositing solutions. — Hydrogen is 
" very apt to be evolved at the cathode in solutions of iron. 
Such liquids also soon spoil for the purpose of electro 
deposition, because they absorb oxygen from the air, and 
become persalts ; and the energy of the electric current, 
instead of being expended in liberating metal, is consumed 
in de-oxidising the solution at the surface of the articles. 
Solutions of ferrous chloride become turbid, and continually 
deposit a slimy precipitate upon the electrodes. Iron solu- 
tions should, therefore, be covered as much as possible from 
the air, but this cannot usually be conveniently done. Klein 
adopted the expedient, of adding glycerine to the liquid, in 
order to retard the change. His solution keeps pretty clear, 
but has upon its surface a slimy foam, which sometimes falls 
upon the articles. 

When iron is deposited from some liquids — for instance, 
one composed of the double chloride of iron and ammonium, 
to which is added a small quantity of glycerine, — after the 
deposit has attained a certain thickness, its surface cracks, 
and brittle spangles are detached and fall to the bottom. 
Deposits of iron should be immersed in boiling water, in 
order to remove dissolved salts, and prevent rusting. 

Properties and uses of electro-deposited iron. — Voltaic iron 
receives magnetism like soft steel. According to W. Beetz, 
iron electro-deposited from a solution containing salam- 
moniac, is, in a very eminent degree, capable of permanent 
magnetism ; and if deposited under the influence of power- 
ful magnets, is itself strongly magnetic. The salammoniac 
is essential to the formation of good electrolytic magnets 
('Telegraphic Journal,' vol. ii. p. 399). 

The earlier formed deposits of iron, were full of holes, and 
quite spongy in texture, in consequence of bubbles of hydro- 



Properties of Electro-deposited Iron. 249 

gen, but by keeping the solutions free from uncombined acid, 
and employing a sufficiently feeble current, that defect has 
been almost entirely obviated. Iron also, in common with 
many other metals in the act of electro-deposition, occludes 
hydrogen (see p. 97). According to R. Leng ('Chemical 
News,' vol. xxi. p. 179), it contains 185 times its volume, 
chiefly in the first layers deposited. According to Troost and 
Hautefeuille (' Chemical News,' vol. xxxi. p. 196), it some- 
times contains as much as 260 times its bulk. L. Cailletet 
states, that by decomposing by an electric current, a neutral 
solution of ferrous chloride, to which salammoniac has been 
added, the iron has been deposited in the form of mammil- 
lary masses, brittle, brilliant, and hard enough to scratch 
glass ; and when the deposit is plunged into water, or other 
liquid, numerous bubbles of pure hydrogen are given off. 
One volume of iron absorbs about 240 volumes of hydrogen, 
and by contact with a flame, the gas ignites, surrounding 
the metal with a pale colour (' Chemical News,' vol. xxxi. 
p. 119 ; 'Journal of the Chemical Society,' vol. xiii. p. 425). 
The advantages of facing printing-type, engraved copper 
plates, those used for printing bank-notes, &c. with iron, are 
very considerable. The iron being very much harder than 
the other metals, is so much the more durable, and is not 
so readily injured by knots in the paper, or by other sub- 
stances accidentally present. It also takes the ink readily, 
and, unlike copper, is not injured by ink containing vermi- 
lion; also, when the iron facing has lost its sharpness of impres- 
sion, it may be dissolved off by means of dilute sulphuric acid, 
without affecting the copper, and a new coating may be put 
on, possessing all the original sharpness ; and this may be 
repeated a very gieat number of times. 

19. Manganese. — Elec.-chem. eqt.= -•?-£= 9-16. Very 

few investigations have yet been made, in the electro deposi- 
tion of the more intractable metals, manganese, chromium, 
uranium, tungsten, molybdenum, vanadium, &c. Junot, in 



250 The Art of Electro- Metallurgy. 

December 1852, took out a patent for 'preparing silicium, 
titanium, tungsten, chromium, and molybdenum, by causing 
them to be deposited from their solutions, by means of 
electric currents, upon metals and other substances ; ' but 
nothing has since been heard of the working of this 
patent. 

The commonest salts of manganese, are the black oxide, 
chloride, and carbonate. The black oxide (pyrolusite), is 
found abundantly as a mineral; contaminated however 
with iron and various earthy matters. The chloride may be 
formed in an impure state, by digesting the black oxide in 
hot and strong hydrochloric acid, and evaporating the solu- 
tion ; or pure, by saturating dilute hydrochloric acid with 
the carbonate ; using pure materials. The sulphate may be 
formed by similar means, using however boiling hot dilute 
sulphuric acid. The chloride and sulphate are pink salts, 
freely soluble in water. 

Deposition of manganese by simple immersion. — Manganese 
is deposited, by the simple immersion of sodium-amalgam, 
in an acidulated solution of a salt of manganese, it then 
alloys with the mercury (Roussin, 'Chemical News,' vol. 
xiv. p. 27). Giles deposited manganese upon mercury, by 
simple immersion of an amalgam of sodium in a saturated 
solution of proto-chloride of manganese ('Philosophical 
Magazine,' 4th series, vol. xxiv.p. 328). According to Phipson, 
magnesium deposits manganese as a black powder, from a 
neutral solution of a proto-salt of that metal. (' Proceedings 
of the Royal Society,' 1864, vol. xiii. p. 217 ; 'Chemical 
News/ vol. ix. p. 219). Magnesium deposits hydrated man- 
ganous oxide from a neutral solution of manganous sulphate, 
but from the same solution acidified, it deposits metallic 
manganese (Commaille, 'Chemical News/ vol. xiv. p. 188). 

Electrolysis of salts of manganese. — Bunsen filled a porous 
cell, with a hot and saturated aqueous solution of chloride 
of manganese, placed it in a charcoal crucible containing 
hydrochloric acid to the same level, put the latter vessel in 



Electrolysis of Salts of Manganese. 251 

a sand-bath (to keep the liquids hot), immersed a platinum 
wire cathode in the centre of the chloride solution, and con- 
nected the charcoal crucible with the positive pole of a four- 
cell Bunsen's battery. Metallic manganese was separated 
with the greatest facility ; but if the density of the current 
at the cathode was reduced, either by enlarging the cathode, 
diminishing the anode, or weakening the current ; or if the 
degree of concentration of the solution was diminished, 
black manganoso-manganic oxide was obtained. ('The 
Chemist,' No. n, August 1854, p. 685 ; Watts' 'Dictionary 
of Chemistry,' vol. ii. p. 438). 

I melted some fluoride of manganese in a platinum 
crucible, and employed two spirals of platinum wire as 
electrodes, and a current from six large Smee's cells. The 
conduction was moderate, and gas was evolved from the 
anode. In a few minutes, both the cathode and the crucible 
became quite rotten, by the union of the deposited man- 
ganese with the platinum. The anode was not corroded. 
I also melted the same salt in a crucible of copper, and 
passed the current by means of a sheet platinum anode, 
and sheet copper cathode, during half an hour. The con- 
duction was free ; abundance of gas was evolved from the 
anode, but none from the cathode, and it ceased on stop- 
ping the current. The deposit on the cathode was black, 
and did not evolve hydrogen with dilute hydrochloric 
acid, and was therefore not metallic manganese. The 
crucible was much corroded at the line of surface of the 
liquid. 

I also electrolysed a dilute solution of fluoride of man- 
ganese, by a current from six Grove's cells, and electrodes of 
platinum. Much heat was evolved, gas was set free at the 
anode, and a film of black deposit formed upon the cathode. 
By similar treatment of a saturated solution of the salt, not 
containing any free hydrofluoric acid, a film of purple 
colour was instantly formed upon the anode, but it dissolved 
quickly, and did not colour the liquid. Gas came from both 



252 The A rt of Electro-Metallurgy. 

electrodes freely ; the liquid also became heated. No solid 
deposit was obtained. 

Salts of manganese yield peroxide at the anode. A so- 
lution composed of one part of chloride of manganese and 
eight of water, yields very beautiful alternating rings of 
purple-green, golden yellow, and blue, surrounded by a 
broad belt of golden yellow. With a solution composed of 
one part of acetate of manganese and fifteen of water, one 
uniform tint is invariably produced, first golden yellow, then 
purple, then green (B. Bottger, ' Poggendorff ; s Annalen,' 
vol. 1. p. 45). 

According to W. Wernicke, solutions of acetate and 
nitrate of manganese, with a feeble current from two 
Daniell's cells, and platinum electrodes, yield a deposit of 
hydrated peroxide of manganese upon the anode ('Journal 
of the Chemical Society,' vol. ix. p. 307). 

20. Chromium. — Elec. chem. eqt.= $^ = 875. The 

ordinary compounds containing chromium, are the sesqui- 
oxide, chromic acid, the two chromates of potash, and 
chrome-alum, i.e. the double sulphate of chromium and 
potassium. The sesquioxide is a substance particularly in- 
soluble in water and acids. The other salts are freely 
soluble in water, and are more conveniently purchased than 
prepared. 

Deposition of chromium by simple immersion. — Mag- 
nesium deposits oxide of chromium from a solution of a 
salt of that metal ; but sodium amalgam shaken up with 
an acid solution of such a salt, becomes an amalgam, 
from which the metal itself may be obtained as a spongy 
mass, by distilling away the mercury in a current of hy- 
drogen. If the amalgam of chromium is heated in the air, 
the particles of chromium scintillate singularly, and the 
amalgam then suddenly becomes incandescent (Roussin, 
' Chemical News,' vol. xiv. p. 27). Magnesium precipi- 
tates hydrated sesquioxide of chromium, from a mixed 



Deposition of Chromium. 253 

solution of chromous and chromic chloride (Commaille, 
'Chemical News,' vol. xiv. p. 188). Vincent deposited 
chromium upon mercury, by simple immersion of sodium 
amalgam in a solution of chloride of chromium j the latter 
metal was then obtained in a finely divided state, by distill- 
ing away the mercury in a retort filled with vapour of 
naphtha ('Philosophical Magazine,' fourth series, vol. 
xxiv. p. 328). 

Deposition of chromium by sepai'ate curre?it. — Bunsen, by 
operating in a similar manner upon a concentrated solution 
of chloride of chromium, as upon one of manganese (see 
p. 250), deposited chromium readily; the deposit presented 
the appearance of iron, but was less affected by damp air ; 
it resisted the action of boiling nitric acid, but dissolved in 
hydrochloric or dilute sulphuric acid. It was friable, and 
presented a high polish on the side next the cathode. On 
diminishing the current, a black powder was deposited, 
containing more oxygen in proportion as the density of the 
current was lessened ; adding protochloride of chromium to 
the solution had a reverse effect, — it caused metallic chromium 
to be deposited ('The Chemist/ No. 11, August 1854, 
p. 686). 

I melted some acid chromate of potassium, and passed 
through it the current from five Smee's elements, by means 
of electrodes of platinum. A deposit slowly formed upon 
the cathode. I also electrolysed a strong solution of 
fluoride of chromium, containing some free hydrofluoric acid, 
and a little hydrochloric acid, by a current from six Grove's 
cells, and platinum electrodes. The liquid soon became 
hot; no gas was evolved from the cathode, but chlorine 
and ozone were set free at the anode, which was not 
corroded. 

21. Uranium. — Elect.-chem. eqt. = = 30. The 

4 
commonest salt of uranium is the sesquioxide, which is a 
yellow powder, insoluble in water, but soluble in several 



254 The Art of Electro-Metallurgy. 

mineral acids. The nitrate, chloride, bromide, and sulphate 
of uranium may be formed, by digesting an excess of the 
sesquioxide in the corresponding diluted acid, until it is 
saturated, and evaporating the solution ; they are each of a 
pale yellow colour, and soluble in water. 

Magnesium deposits golden-coloured hydrated sesqui- 
oxide of uranium, from a solution of oxalate of uranium 
(Commaille, 'Chemical News/ vol. xiv. p. 188). I fused 
some fluoride of uranium in a platinum crucible, and 
added to it some crystals of silicon ; the salt was not de- 
composed. 

Electrolysis of salts of uranium. — I also fused some 
fluoride of uranium in a copper crucible, and passed a 
current from six Smee's cells through it, by means of a 
platinum wire anode, using the crucible as a cathode; a 
little gas was set free at the anode, and the crucible melted. 
A second trial was made, using a platinum crucible, and two 
spirals of platinum wire as electrodes, and the current con- 
tinued during one hour. Conduction was very free, much 
gas was evolved from the anode, but none from the cathode; 
a bulky deposit quickly formed upon the negative spiral, 
especially on the side towards the anode. The deposit 
weighed 43*66 grains, and consisted of hard jet-black crystals. 
The anode was not corroded. In a third trial, four Grove's 
cells were employed, and a special apparatus devised and 
employed to collect the evolved gas, and about five cubic 
inches were obtained. The crystals were not metallic ura- 
nium ; they were insoluble in boiling water, but soluble in 
cold dilute hydrofluoric acid, without evolving gas. About 
one-fourth of the deposit, consisted of a fine crystalline 
powder, nearly of the colour of copper, but darker, and 
was composed of the crystals, with a film of less reduced 
fluoride upon them ; they evolved gas in cold nitric acid, 
or in hot dilute nitric acid. They were not fused by heat- 
ing alone to redness upon platinum foil ; but if caustic 
potash was added, they oxidised. I also electrolysed a 



Electrolysis of Tungstate of Sodium . 255 

fused mixture of the pure fluorides of uranium and potas- 
sium, with platinum electrodes ; the results were very 
similar, except that the deposit upon the cathode fell off as 
fast as it was formed ; and the crystals had to be extracted 
by dissolving the cooled saline mass in slightly diluted and 
hot hydrochloric acid ; they were very much like those 
of silicon; their form was that of a short pyramid with a 
square base. The anode was very slightly corroded and 
made bright by the action ; and twenty cubic inches of gas 
were collected from it. 

I also electrolysed a strong aqueous solution of fluoride 
of uranium, with a current from six Grove's cells, and plati- 
num electrodes. Much gas, having the odour of ozone, was 
evolved from the anode, and the liquid became hot. I then 
added some aqueous hydrofluoric acid ; the conduction was 
very free, and abundance of gas evolved from each electrode, 
but no solid deposit was formed. 

22. Tungsten. — Elec. chem. eqt.= — ~- = 30-C6. The 

6 

only readily available salts of this metal, are tungstic acid, 
and tungstate of sodium ; the former is a yellow powder, 
insoluble in water and in acids ; the latter is a colourless 
salt, soluble in water. 

I fused some tungstate of sodium to a clear liquid 
in a porcelain vessel, and electrolysed it by means of a 
current from five Smee's cells, a gas-carbon anode, and a 
platinum wire cathode. The conduction was moderately 
free, gas was evolved from the anode, and at the cathode, 
black matter was set free, which floated, and became diffused 
in the liquid, and partly re-dissolved. 

23. Molybdenum. — Elec. -chem. eqt.= ?—- = 16. The 

only common salts of this metal, are molybdic acid, sulphide 
of molybdenum, and molybdate of ammonium. Molybdic 
acid may be prepared, by digesting sulphide of molybdenum 
in strong nitric acid \ it is a pale yellow powder, insoluble in 



2 56 The A rt of Electro -Metallurgy. 

water. The sulphide is a mineral substance, looking like 
black-lead, and insoluble in water. The moljbdate of 
ammonium is white, and sparingly soluble in water. 

Electrolysis of molybdic acid. — I fused some molybdic 
acid in a porcelain crucible, and passed the current from five 
Smee's cells through it, by means of a gas-carbon anode, and 
platinum cathode. It conducted freely. The action was 
rather strong at the anode, but little gas was evolved. Black 
crystals quickly collected round the cathode, but no gas was 
set free with them ; the entire liquid soon became full of 
the crystals, which spread quickly to the anode. The carbon 
was not dissolved, or disintegrated. The cooled residue 
was a solid black mass of crystals, which dissolved sparingly 
in water, and formed a blue liquid. In a second experiment, 
using twelve large Smee's elements, and platinum anode and 
cathode, there was free action, and much gas evolved ; and 
the bluish-black deposit quickly formed upon the cathode. 
Most of the gas came from the anode. A large quantity of 
crystalline needles (|th to |th of an inch long), formed upon 
the cathode, and stood out at right angles to its surface in the 
fused substance. The deposit imparted a transient green 
colour to water. 

Molybdic acid dissolved freely in pure hydrofluoric acid, 
evolving a little heat. The solution was electrolysed, both 
with a carbon and with a platinum anode. The colourless 
liquid conducted freely a current from ten large Smee's cells, 
became instantly blue, and almost black, at a platinum cathode. 
Gas was evolved at each electrode, that from the gas-carbon 
anode was the most abundant, and had a slightly chlorous 
odour. On stopping the current, the deep blue film on the 
cathode quickly dissolved, and the liquid soon became 
colourless. During the action, the cathode was several times 
removed from the electrolyte, and dipped into water; much 
blue matter dissolved, but the water became nearly colour- 
less in half a minute, even without stirring, and however 
large the quantity of blue matter was, which dissolved in it. 



Deposition of Lead by Simple Immersion. 257 

24. Vanadium. — Elec.-chem. eqt. = - ^J- — 228. The 

6 

only readily attainable compounds of this element, are 
vanadic acid, and vanadate of ammonium. I electrolysed 
a solution composed of vanadic acid dissolved in pure 
dilute hydrofluoric acid, with a gas-carbon anode and plati- 
num cathode, and ten Smee's cells. Gas having an odour 
of ozone was evolved from the anode. I also saturated 
dilute sulphuric acid with pure vanadate of ammonium, and 
electrolysed it with platinum electrodes, and a current from 
four platinum and zinc elements. The conduction was very 
sparing ; the solution became gradually of a very intense 
bluish-black colour from action at the cathode, and a jet- 
black powdery deposit of some thickness formed upon that 
electrode. 

2$. Lead. — Elec.-chem. eqt. = —L = 103-5. The com. 

monest salts of lead, besides its three oxides, viz. litharge, 
red-lead, and peroxide of lead, are the nitrate, chloride, car- 
bonate, sulphate, and acetate. All of these may be readily 
purchased in a comparatively pure state. The nitrate and 
acetate, are the two common soluble salts of the metal ; the 
others may be readily made, by dissolving litharge, red-lead, 
or carbonate of lead, in the particular acids, to saturation, 
and evaporating the solutions. 

Deposition of lead by simple immersion. — (See also p. 79.) 
— The old experiment of producing a lead tree, by suspending 
a spiral of zinc wire in a solution of nitrate or acetate of 
lead, is well known. According to A. Cossa, aluminium 
slowly deposits lead in crystals, from a solution of plumbic 
nitrate or acetate, and immediately from a solution of the 
chloride. An alkaline solution of plumbic chromate, is also at 
once decomposed by that metal, with separation of metallic 
lead, and formation of chromic oxide (Watts' ' Dictionary of 
Chemistry/ vol. vii. p. 54). Magnesium deposits lead and 
oxychloride of lead, together with much hydrogen, from a 



258 The A rt of Electro-Metallurgy. 

neutral solution of plumbic chloride (Commaille, ' Chemical 
News,' vol. xiv. p. 188). 

I melted some plumbic fluoride in a platinum crucible, 
and added some crystals of boron ; metallic lead was 
separated with vivid incandescence, and made a hole in the 
crucible. Crystals of silicon also exhibited incandescence, 
and set free metallic lead. Metallic antimony or copper, did 
not liberate lead from the fused fluoride. By stirring the 
melted fluoride with an iron rod, the latter was rapidly cor- 
roded, heat being evolved, and lead deposited. Metallic 
aluminium behaved similarly, but more rapidly. Zinc ex- 
ploded, and magnesium detonated, under similar circum- 
stances. The latter is a dangerous experiment. 

Articles of zinc or tin, but not of iron, become coated 
with lead by simple immersion, in a liquid formed by boiling 
litharge in a solution of caustic potash. Those of iron, 
but not of copper, coat themselves with lead by mere im- 
mersion, in a solution of plumbic acetate, i.e., sugar of lead. 

Deposition of lead by contact with a second ?netal. — (See 
also p. 83.) — F. Weil coats articles with lead, by a similar 
process to that he employs for tin (see p. 266 ), using a salt 
of lead instead of one of tin. And to produce a deposit of 
lead free from zinc, he uses similar means to those described 
for tin (' Chemical News,' vol. xiii. p. 2). According to 
Becquerel, if a piece of bright copper in contact with zinc, 
be immersed in a solution of chloride of lead and sodium, 
the copper becomes covered with lead (' Chemist/ vol. v. 
p. 408). I connected together a wire of zinc, and one of 
platinum, and immersed them in a solution of litharge in 
aqueous ammonia; both became coated with a black 
powder in a few minutes. The deposit, moist with the liquid, 
became yellow by contact with the air, and was apparently 
re-converted into litharge. 

Haeffelly coats copper or brass with lead, by immersing 
it in contact with a bar of tin, in a hot alkaline solution of 
oxide of lead. The tin dissolves in the form of an alkaline 



Deposition of Lead by Separate Current 259 

stannate, but the lead is precipitated in a spongy state 
(' Chemical News/ vol. vi. p. 163). 

Deposition of lead by separate current. — (See also p. 89.) 
— According to Faraday, fused protoxide of lead yields metal 
at the cathode, and oxygen at the anode ; the chloride gives 
lead at the cathode, and chlorine at the anode; and the borate 
liberates metal at the cathode, and oxygen and boracic acid 
at the anode. Beetz electrolysed fused plumbic fluoride, and 
observed that a colourless gas was evolved from the positive 
pole, and lead set free at the negative pole (' Poggendorf's 
' Annalen ; ' also ' The Chemist,' new series, vol. i. p. 253) 
Fremy also electrolysed it in a platinum vessel, and found 
it easily decomposed, the lead was set fiee, and alloyed with 
the vessel (' Chemist,' new series, vol. ii. p. 548). I also 
electrolysed 400 grains of pure fluoride of lead (melted in 
a thick copper crucible), with a current from six Smee's 
cells, using a platinum wire as an anode, and one of copper 
as the cathode; conduction was copious, and a bulky crust 
quickly formed upon the cathode, and advanced towards the 
anode in lumpy projections. A little gas appeared at the 
latter, but during a short time only. The deposit upon the 
cathode was not lead, nor was there any metal contained 
in a free state in it, or in the saline mass, after action lasting 
one hour ; it was a mass of lead-salt, brittle, and of a red- 
brown colour (like that of peroxide of lead), when cold. 
The conduction was very perfect, and the fused salt appeared 
to conduct without being decomposed. The anode was not 
corroded. I also electrolysed the fused salt in a deep, 
narrow, and thick copper cup, with an anode of gas-carbon, 
during one and a quarter hours ; the latter was corroded, and 
the metal liberated; action was copious, gas was evolved 
at the anode, and about seven or eight cubic inches were 
collected. G. J. Knox also electrolysed fused fluoride of 
lead with an anode of charcoal, a platinum wire cathode, 
and a current from sixty voltaic cells (' Philosophical 
Magazine,' third series, vol. xvi. p. 192). 

s 2 



2 60 The A rt of Electro-Metallurgy. 

Lead may be deposited from an aqueous solution, either 
of its nitrate or acetate, by means of a separate current, 
with an anode of lead ; also from a liquid, formed by satu- 
rating a boiling solution of caustic potash with litharge ; but 
it is difficult to obtain any considerable thickness of reguline 
metal from either of these liquids. The nitrate and acetate, 
yield peroxide of lead at the anode. 

Deposition of peroxide of lead. — Electro-chromy. — -Accord- 
ing to W. Wernicke, an alkaline solution of the tartrate 
of lead and sodium, with platinum electrodes, and a cur- 
rent from two Daniell's cells, yields a black deposit of 
peroxide of lead upon the anode ; and a solution of one 
part of plumbic nitrate and eight of water, gives a similar 
deposit by such treatment (' Journal of the Chemical 
Society,' vol. ix. p. 306 ; ' Chemical News,' vol. xxii. p. 
240). 

Nobili in the year 1826, discovered, that if a solution of 
acetate of lead be electrolysed, by means of a large sheet 
platinum anode, and a platinum wire cathode, a deposit is 
formed upon the positive plate ; and that if a polished steel 
plate be employed as the anode, with a current from four or 
six Grove's cells, the deposit is in the form of a thin film, and 
exhibits all the colours of the spectrum ; and by placing the 
positive plate horizontally beneath the vertical negative wire, 
the colours were in the form of rings, the centre of which was 
the wire, and were arranged in the order of the chromatic 
scale. These colours are known as ' Nobili's rings.' Becque- 
rel, Gassiot, and others, have, by varying the strength of the 
battery, and of the solutions employed, and interposing non- 
conducting patterns between the anode and cathode, and by 
using cathodes of different shapes, obtained effects of great 
delicacy and beauty. Salts of other metals, such as man- 
ganese, bismuth, cobalt, nickel, &c, which yield deposits of 
peroxide of the anodes (see pp. 112, 235, 242, 252), may be 
employed instead of those of lead. Becquerel obtained films 
of peroxide of iron, by electrolysing in vacuo, a solution of 



Electro- Chromy. 261 

protoxide of iron in liquid ammonia (' Chemist,' vol. iv. 

P- 457)- 

The colours occur, sometimes upon the anodes, and 
sometimes upon the cathodes, according to the liquid 
employed, and with a variety of metals in a number of dif- 
ferent liquids. At other times, they arise wholly from deposits 
from the liquid, as with peroxides on anodes of platinum, 
or films of metal upon the cathodes ; and sometimes they con- 
sist of insoluble substances, formed by the union of the anode 
with an element of the liquid. 

Becquerel prepared his plumbic solution as follows : — 
Dissolve 200 grammes of caustic potash in two quarts of 
distilled water, add 150 grammes of litharge, boil the 
mixture half an hour, allow it to become clear, take the clear 
portion, and dilute it with its own bulk of water (' The 
Chemist/ vol. iv. p. 457). The solution is used cold, and 
is rapidly deprived of its metal, because lead is deposited 
upon the cathode at the same time. 

By this means may be imparted to polished surfaces of 
metals, all the richest colours of the rainbow. 'They 
commence with silver blonde, and progress onwards to fawn 
colour, and thence through various shades of violet to the 
indigo and blues ; then through pale blue to yellow and 
orange ; thence through lake and bluish lake to green and 
greenish orange, and rose orange ; thence through greenish 
violet and green, to reddish yellow and rose lake, which is 
the highest colour on the chromatic scale ' (Walker's ' Electro- 
type Manipulation/ part ii. 16th edition, p. 40). Too great a 
strength of the current covers all the tints with a uniformly 
dark brown coating. The deposits, if properly prepared, 
resist friction well. 

Metallo-chromy, effected by means of a solution of oxide 
of lead in caustic soda or potash, is largely employed in 
Nuremberg, to ornament metallic toys (Wagner's 'Tech- 
nology/ p. 117). Bells are similarly coloured in France, 
and the hands and dials of watches in Switzerland. 



262 The Art of Electro-Metallurgy. 

26. Thallium. — Elec. -chem. eqt. = 204. Solutions of 
this metal are easily formed, by making a piece of it 
the anode, for a sufficient length of time, in the respective 
acids, sufficiently diluted to dissolve the compounds. The 
sulphate is one of the most soluble salts, and requires about 
twenty times its weight of water to dissolve it. 

According to A. Cossa, aluminium deposits metallic thal- 
lium from a hot solution of its chloride (' Watts's Dictionary 
of Chemistry,' vol. vii. p. 54). Zinc coats itself with metal in 
solutions of salts of thallium, but tin does not. Accord- 
ing to Lamy, zinc precipitates it from the solution of 
the sulphate and nitrate, in the form of brilliant crystalline 
laminae. I found that crystals of silicon had no reducing 
effect, upon a solution of fluoride of thallium, containing free 
hydrofluoric acid. 

Electrolysis of salts of thallium. — Solutions of the salts of 
thallium are easily decomposed by a feeble electric current; 
and the metal deposited in the form of beautiful crystalline 
plates upon the cathode. When one of the sulphate is 
electrolysed by a weak current, brown thallic peroxide is 
deposited upon the anode. 

I electrolysed an aqueous solution of the fluoride, by 
means of one Smee's cell, a thallium anode, and a platinum 
cathode. It conducted freely, and quickly yielded a deposit 
of the metal, in long feathery crystals, like those of electro- 
deposited tin, but of a less white colour. 

Thallium deposits metal from the sulphate, nitrate, and 
acetate of copper, nitrate of silver, solutions of gold, mer- 
curous sulphate, and acetate of lead, but a basic salt from 
nitrate of cobalt (W. C. Reid, ' Chemical News/ vol. xih 
p. 242). 

27. Indium. — Elec.-chem. eqt. = TI3 4 = 37*8. This 

3 

metal being at present very costly, little has been done with 
it in electro-metallurgy. It is allied to thallium and aluminium. 
Its salts are generally freely soluble in water ; the double 



Salts of Tin. 263 

sulphate of indium and potassium, called indium-alum, dis- 
solves in half its weight of water at 1 6° C. 

Indium is precipitated as metal from the solutions of its 
salts, by means of zinc. A solution of the sulphate or chlo- 
ride, may be used for this purpose. 

28. Tin. Elec. chem. eqt. = — = 29-5. The com- 
monest salts of tin, are stannous and stannic oxides, the 
two chlorides, the sulphides of tin, and the stannates of 
sodium and potassium. Stannous chloride is the most use- 
ful salt, and should be freshly prepared, because it becomes 
less soluble by being kept a long time exposed to the air ; it 
may be easily made, by adding abundance of fragments of 
pure tin to strong hydrochloric acid, and keeping the acid hot, 
until it has acquired an oily consistence, and gas ceases to 
be evolved. Stannic oxide maybe prepared, by pouring the 
anhydrous bichloride very gradually into water, with stirring, 
and then adding sufficient ammonia to precipitate the oxide. 
Wash the precipitate. 

A protochloride of tin depositing liquid, may be easily 
formed, by dissolving the ordinary commercial salt in water, 
and adding a little hydrochloric acid, to remove any cloudi- 
ness which may appear ; a similar, but better liquid, may be 
made by the battery process, by passing the current through 
dilute hydrochloric acid, by means of a large tin anode, until 
sufficient metal is dissolved. This (or the other chloride of 
tin) is not a good solution to obtain reguline metal from ; 
it has a very great tendency to deposit the tin in the form 
of long crystalline needles, of a fernlike appearance, which 
often project from the corners and edges of the cathode, to 
a distance of upwards of half an inch. A solution composed 
of eleven ounces of water, one of hydrochloric acid, and 
eighty grains of protochloride of tin, admits of this effect 
being produced in a striking manner. Nearly all the com- 
pounds of tin, and especially those formed with mineral 
acids, exhibit this tendency in a greater or less degree, when 



264 The Art of Electro- Metallurgy. 

acted upon by electrolysis, rendering the deposition of tin in 
thick layers of fine white coherent metal, a matter of con- 
siderable difficulty. 

The stannate of potash solution is made, either by dis- 
solving the solid salt in water, or mixing freshly precipitated 
peroxide of tin (whilst still moist) with a boiling solution 
oi caustic potash. It may also be easily formed by the battery 
process, by passing a strong current of electricity, by means 
of a large tin anode, through a strong and boiling solution of 
caustic potash, until the immersed cathode receives a free 
white deposit. This solution, if used at 150 Fahr., yields 
fine white tin ; but it decomposes by exposure to the 
atmosphere, and soon deposits its metal as oxide, at the 
bottom of the vessel. A solution of cyanide of potassium 
and of tin, has been proposed as a depositing liquid ; but 
it is a bad conductor with a tin anode, even if hot, and does 
not dissolve the metal freely. 

Electrical relations of ti?i and iron. — Tin is feebly 
negative to iron at all temperatures between 62 and 203 
Fahr. in distilled water, and positive to it at 212 Fahr. It 
is positive to iron at all temperatures between 62 and 212 
Fahr. in a saturated solution of boracic acid ; also the same 
between those temperatures, in a strong solution of phos- 
phoric acid in distilled water, or in one measure of oil of 
vitriol, mixed with either nine or ninety-six of distilled 
water ; or in a mixture of one measure of this acid, and 192 
of distilled water, from 73 to 15 8° Fahr., and negative to 
iron above that to 212 Fahr.; it is positive to iron from 72 
to 2i2° Fahr. in a mixture of equal measures of hydro- 
chloric acid and water • it is negative to iron from 70° to 
77 Fahr., and positive above that to 212 Fahr., in a mixture 
of one measure of hydrochloric acid, and nine of distilled 
water; it is negative to iron from 70 to 212 Fahr. in a 
mixture of one measure of hydrochloric acid, and ninety 
of distilled water, and positive to iron from 68° to 212 
Fahr., in one measure of hydrofluoric acid, and nine of 



Deposition of Tin by Simple Immersion. 26$ 

water; it is positive to iron in one measure of nitric acid, 
and nine of water from 70 to in Fahr., and negative 
from in to 212 Fahr. ; and it is positive to iron from 82 
to 212 Fahr. in a mixture of one measure of nitric acid, 
and ninety-six of water. 

Deposition of tin by simple immersion. — (See also p. 79.) 
— I found that crystals of silicon, did not deposit tin from a 
solution of stannous fluoride containing free hydrofluoric 
acid; and that zinc immersed in a solution of stannic 
fluoride, evolved gas, and produced a flocculent precipitate. 

A remarkable instance of deposition of tin, is mentioned 
by M. Henri Loewel. He added metallic tin to a solu- 
tion of green crystallised chloride of chromium (which did 
not contain an excess of acid), in a closed glass vessel, 
and boiled the mixture ten or twelve minutes, and allowed 
it to cool. During the heating, the tin dissolved, and took 
chlorine from some of the chromium salt, forming proto- 
chloride of tin and protochloride of chromium. But during 
the cooling, a reverse action occurred, the protochloride of 
chromium removed the chlorine from the other protochloride, 
and the tin was deposited in the form of numerous small 
metallic plates (' The Chemist,' part viii. May, 1854, p. 476). 

Magnesium deposits stannic acid, and spongy tin, from 
a solution of stannous chloride (Commaille, 'Chemical 
News,' vol. xiv. p. 188). A tin tree, is produced by immer- 
sing a rod of zinc, or a spiral of zinc wire, in ten or twenty 
ounces of water to which have been added three drachms of 
stannous chloride, and ten drops of nitric acid, and allowing 
the liquid and zinc to remain undisturbed. 

To coat brass pins, and other small articles of copper or 
brass, with tin, they are placed in layers between sheets of 
grain tin, in a saturated solution of cream of tartar, and the 
liquid boiled. A little stannous chloride may also be added 
if necessary. 

Clean articles of copper, bronze, or brass, in contact 
with cuttings of tin, in a boiling solution of peroxide of tin 



266 The Art of Electro-Metallurgy. 

in caustic potash, become coated in a few minutes with a 
beautiful layer of metal. The solution may also be used for 
tinning iron, by the battery process, with large anodes of tin, 
and may be made to give a very fine deposit, but it precipi- 
tates its metal gradually, in the form of a white powder, by 
contact with the air (see p. 264). 

C. Paul tins articles of zinc, iron, brass, copper, &c, in the 
following manner : — The zinc or iron articles, are immersed 
in a mixture of ten parts of water, and one of sulphuric 
or nitric acid, and a dilute solution of cupric sulphate is 
then slowly added, with stirring. After a thin layer of cop- 
per is deposited, the articles are removed, washed, wetted 
with a solution, composed of one part of crystals of stannous 
chloride, two of water, and two of hydrochloric acid, and 
then shaken with a mixture of finely powdered chalk, and 
sulphate of copper and ammonium, which is prepared by 
dissolving one part of cupric sulphate in sixteen of water, 
and adding aqueous ammonia, until a clear dark blue liquid 
is formed. The articles are now tinned by immersion in a 
solution, composed of one part of crystals of stannous chlo- 
ride, and three of white argol, dissolved in water (' Journal 
of the Chemical Society,' vol. xi. p. 955). 

To coat articles of iron or zinc with tin, dissolve one 
part of fused stannous chloride, and thirty of ammonium- 
alum, in 2,000 of water, heat the solution to boiling, and 
immerse the previously cleaned articles in it until they 
attain a fine white colour; add to the solution as it becomes 
weaker, small quantities of the stannous chloride. Accord- 
ing to Roseleur, articles of zinc may also be tinned by sim- 
ple immersion, in a solution composed of one part of fused 
stannous chloride, and five of pyrophosphate of sodium, 
dissolved in 300 of distilled water. Tin which has been 
dissolved from the surface of tinned iron, is sometimes 
reduced to metal, by immersion of pieces of zinc in the 
solution. 

According to Becquerel, copper, and iron, do not coat 



Electro-Deposition of Tin. 267 

j themselves with tin, in a dilute solution of the double chlo- 
j ride of tin and sodium, at 160 Fahr., but are readily tinned 
i in that liquid by contact with zinc (' The Chemist/ vol. v. 
! p. 4°S)- 

Depositing tin by contact with a second metal. — (See also 
p. 83.) — For coating articles of iron with tin, by means of 
contact with zinc, Roseleur recommends the two following 
liquids: — No. 1. Take equal weights of distilled water, stan- 
nous chloride, and cream of tartar, dissolve the tin salt in 
one-third of the cold water, warm the remainder of the water, 
dissolve the cream of tartar in it, and mix the solutions ; 
the liquid is clear, and has an acid reaction. No. 2. Dis- 
solve six parts of crystals, or four of fused stannous chlo- 
ride, and sixty of pyrophosphate of potassium or sodium, 
in 3,000 of distilled water, and stir the mixture ; the liquid 
is clear. Each solution is used hot, and kept in constant 
motion. The articles are immersed in contact with fragments 
of zinc, the total amount of surface of which is about ^-th 
that of the articles. The process of deposition occupies from 
one to three hours. Equal weights of pyrophosphate, and of 
fused stannous chloride, are added occasionally. 

According to F. Weil, copper, and coppered metals, as 
well as iron and steel, may be tinned, by dissolving a salt of 
tin in a strong solution of potash or soda, and immersing the 
articles in the liquid in contact with zinc ; the solution being 
at from 50 to ioo° C. : the deposit, however, contains zinc 
To obtain a pure deposit, of increasing thickness, place in 
the vessel containing the tin solution, a porous cell contain- 
ing the alkaline liquid (without tin-salt) and the zinc. Put 
the article to be tinned, in the outer liquid, and connect it 
with the zinc by a wire. To revive the inner liquid, precipi- 
tate the dissolved zinc, by addition of sulphide of sodium 
('Chemical News,' vol. xiii. p. 2). 

Dr. Hillier uses for tinning metals, a solution composed 
of one part of stannous chloride and twenty of water, 
to which is next added a solution of two parts of caustic 



2 68 The A rt of Electro-Metallurgy. 

soda, in twenty of water; the mixture is heated. The articles 
are placed upon a perforated plate of block tin in the hot: 
liquid, and agitated with a rod of zinc until they are suffi- 
ciently coated (' Chemical News/ vol. xx. p. 84). \ 

Tinning iron wire: by M. Heeren. — The wire is first: 
cleaned in a hydrochloric acid bath in which a piece of zinc is| 
suspended. The cleaned wire is then brought into contact!: 
with a plate of zinc, in a bath in which two parts of tartaric |i 
acid are dissolved in 100 of water, with further addition of 
three parts of stannous chloride, and three of soda ; and 1 
after remaining about two hours in the liquid, the wire is 1 
brightened by drawing it through a hole in a steel plate 
('Journal of the Chemical Society/ vol. xiii. p. 672). 

F. Stolba uses, for tinning, a carefully made solution of 
protochloride of tin, containing from 5 to 10 per cent of that: 
salt, to which mixture a small pinch of cream of tartar 
has been added. The article, previously well cleaned, is \ 
rubbed over with the solution, and then with powdered zinc ; 
it is then washed, and polished with soft whiting (' Chemical < 
News/ vol. xxiii. p. 21). 

According to Raoult, gold or copper in contact with tin, 1 
in a concentrated and boiling solution of stannous chloride, 
receives a deposit of tin. But gold in contact with iron, 
nickel, antimony, lead, copper, or silver, receives no such \ 
coating, either in the hot or cold solutions (' Chemical News,' 
vol. xxvi. p. 240 ; vol. xxvii. p. 59; ' Journal of the Chemical \ 
Society/ vol. xi. p. 464). I 

Electrolysis of salts of tin. — Fused stannous chloride, ! 
yields tin at the cathode, and stannic chloride escapes in ; 
vapour at the anode (Faraday). Fremy electrolysed fused 
fluoride of tin in a platinum vessel; it was easily decomposed ; « 
but the deposited metal alloyed with, and perforated, the 
vessel in a few minutes (' The Chemist/ new series, vol. ii. 
p. 548). Anhydrous tetrachloride of tin did not conduct a 
current from 8,040 cells of W. de la Rue's chloride of silver 
battery (' Proceedings of the Royal Society/ vol. xxv. p. 325). 



Deposition of Crystals of Tin. 269 

I electrolysed a saturated non-acid solution of stannous 
fluoride, by means of large platinum electrodes, and a current 
from ten large Smee's elements ; the conduction was sparing j 
a little oxygen was evolved from the anode, and long feathery 
crystals of tin were slowly formed upon the cathode. No 
gas was evolved from the cathode, nor deposit formed upon 
the anode. In another experiment, with one Smee's cell, and 
a copper cathode, the deposit of tin was white, and beautiful 
crystals of the metal soon reached across the liquid and 
touched the anode. 

By passing a current from six Grove's elements, by means 
of platinum electrodes, through a strong solution of stannic 
fluoride, containing little or no free hydrofluoric acid, a grey 
deposit of metallic tin soon occurred. There was free con- 
duction, much gas from the anode, and heat evolved in the 
liquid. The anode was not corroded nor received any solid 
deposit. 

To obtain crystals of tin by electrolysis. — The crystallisa- 
tion of tin, is a phenomenon conspicuously striking, under 
some conditions, in a solution of stannous chloride. The 
crystals of tin formed upon the cathode, increase so rapidly 
in length, as to grow across the solution, and touch the posi- 
tive pole in a few minutes. And if the solution and current 
are strong, and the cathode small, quite a mass of crystals 
will soon fill the liquid, and converge towards the anode. 
If the anode be drawn farther away in the solution, the 
crystals follow it. The largest crystals are produced by 
slow action : to produce them, a platinum capsule is covered 
with an outer coating of wax, leaving the bottom uncovered, 
and then set upon a plate of amalgamated zinc in a porcelain 
vessel. The capsule is then filled completely with a dilute 
and not too acid solution of stannous chloride, whilst the 
outer vessel is filled with water (containing one-twentieth its 
bulk of hydrochloric acid), up to such a height, that the two 
liquids come into mutual contact. The electric current 
generated, reduces the salt of tin, and in a few days the crys- 



2 yo The A rt of Electro-Metallurgy. 

tals upon the interior of the capsule are well developed, and 
should be washed with water and dried quickly (F. Stolba, 
Chemical News,' vol. xxx. p. 177). 

Deposition of tin by separate current process. — (See also 
p. 89.) — There are many solutions for electro-tinning by 
means of a separate current, but only a very few have been 
extensively used. Most of them alter in property by contact 
with the atmosphere, and deposit their metal as a white 
oxide. Roseleur uses a solution, composed of five parts of 
fused (or six of crystals) stannous chloride, and fifty of pyro- 
phosphate of potassium or sodium, added to 5,000 of ! 
distilled water ; the chloride is dissolved in a portion of the 
water, and added the last, and the liquid is stirred until it is 
clear. A very large surface of anode is employed, and a 
strong electric current. As less tin is dissolved than is depo- 
sited, it is necessary to add occasionally, equal weights of the 
pyrophosphate and fused chloride. 

Fearn's patent process for tinning, has been worked in 
Birmingham. The liquids employed are prepared as fol- 
lows : — 

No. 1. A solution of stannous chloride (not containing 
much free acid) is first made, containing three ounces of 
metallic tin per gallon. Thirty pounds of caustic potash 
are also dissolved in twenty gallons of water, and thirty 
ot pyrophospnate of sodium in sixty gallons of water. Two 
hundred ounces by measure of the tin solution, are poured 
slowly (whilst stirring with a glass rod) into the twenty 
gallons of potash liquid ; the precipitate formed re-dissolves 
quickly; into this liquid is poured, first all the cyanide 
solution, and then all the pyrophosphate, and the mixture 
stirred. 

No. 2. Fifty-six pounds of salammoniac are dissolved 
in sixty gallons of water, and twenty of pyrophosphate of 
sodium in forty gallons of water ; and into the latter is poured 
100 ounces by volume of the chloride of tin solution, and 
the mixture stirred j the precipitate soon re-dissolves. The 



Electro-Deposition of Tin. 271 

salammoniac solution is then added to the mixture, and the 
whole stirred. 

No. 3. One hundred and fifty pounds of salammoniac 
are dissolved in 100 gallons of water ; and 200 fluid ounces 
of the tin solution poured into it, and the mixture well stirred. 

No. 4. Four hundred ounces of tartrate of potassium, are 
dissolved in fifty gallons of water, and 1,200 ounces of solid 
caustic potash in another fifty gallons ; 600 fluid ounces of 
the tin solution are then added slowly, with stirring, to the 
liquid tartrate ; and then the caustic potash solution poured 
into the mixture, with continual and thorough agitation, to 
re-dissolve all the precipitate. 

The first solution is used at 70 Fahr. with a current from 
two Bunsen's cells. The second is worked at ioo° to no° 
Fahr. with a weaker current. The third is used at 70 Fahr. 
And the fourth solution may be used cold. The first and 
fourth solutions, yield thick deposits, without requiring alter- 
nate deposition and scratchbrushing. As during working, 
more tin is deposited than dissolved, the oxide or other com- 
pound of the metal, must be added occasionally, except in 
the case of the third solution, which acts upon the anode more 
freely than the others. Articles of cast iron require to be 
covered with a thin film of copper, previous to being tinned 
in these liquids. Articles of zinc are tinned in No. 1 solu- 
tion. Further particulars respecting the means necessary for 
keeping each particular mixture in proper working order, are 
given in the specification of the patent. The process is 
worked by the ' Electro-stannous Company/ in Birmingham. 

Mr. Joseph Steele, coats zinc, iron, steel, copper, and 
brass, with tin, in his patent solution, by the battery process, 
thus : — Dissolve sixty pounds of common soda, fifteen 
of pearlash, five of caustic potash, and two ounces of cyanide 
of potassium, in seventy-five gallons of water, and filter the re- 
sulting solution ; then add two ounces of acetate of zinc, and 
sixteen pounds of peroxide of tin ; stir the resulting mixture 
until all is dissolved ; it is then ready for use. Work it 



2J2 The Art of Electro-Metallurgy. 

by means of a separate current, with an anode of tin, keeping 
the liquid at 75 Fahr. 

De Lobstein's patent solution, for tinning by means of 
the battery, is composed of 500 gallons of water, eighty 
pounds of caustic soda, thirty-four ounces of cyanide of 
potassium, and twenty- two of salts of tin, i.e., stannous 
chloride. 

The acetate and oxalate of tin, also oxide of tin dissolved 
in a solution of cyanide of potassium, have been tried for 
tinning, but do not appear to yield satisfactory results, 

Processes of electro-tinning are not extensively used, be- 
cause there appears to be no great demand for electro-tinned 
articles. 

Elect7'o-depositioii of alloys of copper and tin. — A colour 
similar to that of bronze, is imparted to articles of iron or steel, 
by agitating them for a long time, in a solution composed of 
four to five parts of sulphate of copper, and four to five of 
crystallised stannous chloride, dissolved in 100 of water. 

F. Weil coats articles of iron, steel, and other metals, 
with true bronze [i.e., an alloy of copper and tin), by adding 
to his tartrate of copper bath (see p. 204), some stannate of 
sodium, or a solution of chloride of tin previously treated with 
a sufficiency of soda ; and immersing the articles in the 
mixture in contact with zinc (see ' Chemical News/ vol. xiii. 
p. 2). Salzede patented (Sept. 30, 1847) a liquid for depo- 
siting bronze by the battery process ; it consists of carbonate 
of potassium, chloride of copper, chloride of tin, nitrate of 
ammonium, and cyanide of potassium, dissolved in water, and 
used at a temperature of 77 Fahr. A solution patented by 
Newton (July 29, 1850), for a similar purpose, consists of the 
tartrates of copper, tin, and potassium. 

M. Weis-Kopp imparts a bronze appearance to electro- 
coppered articles of cast iron, by rubbing them with a mix- 
ture of four parts of salammoniac, one of oxalic, and one 
of acetic acid, dissolved in thirty of water (' Chemical News,' 
vol. xxi. p. 47). 



Deposition of Cadmium. 273 

29. Cadmium. — Elec- chem. eqt =ii^-= 56-0, The 

most usual salts of cadmium, are the oxide, nitrate, chloride, 
bromide, iodide, sulphide, and sulphate. The nitrate, chlo- 
ride, iodide, bromide, and sulphate, are colourless, and 
may be easily prepared, by saturating the respective acids, 
with either cadmium or its oxide, and evaporating the solu- 
tions until they crystallise. Fluoride of cadmium may be 
made, by adding the carbonate to an excess of dilute 
hydrofluoric acid, and evaporating the mixture to dryness. 
I have found that crystals of silicon, heated with this salt, 
separate the metal. 

From a solution of the chloride, magnesium deposits, 
with strong action, a mixture of cadmium and an oxy- 
chloride of that metal. (Commaille, ' Chemical News,' 
vol. xiv. p. 188.) 

Deposition of cadmium by contact zvith another metal. — 
According to Raoult, gold, or copper, in contact with cad- 
mium, in a concentrated and boiling solution, of cadmium 
sulphate, or chloride, decomposes these salts, and quickly 
deposits a white, brilliant, and firmly adherent, but thin film 
of cadmium, upon the gold or copper, even when the solution 
is not acidulated and no hydrogen is evolved. The experi- 
ment does not succeed with the nitrate. But gold, in 
contact with iron, nickel, antimony, lead, copper, or silver, 
in cold or boiling, acid or neutral, solutions of salts cf 
cadmium, receives no such deposit ('Chemical News,' 
vol. xxvi. p. 240; vol. xxvii. p. 59; 'Journal of the 
Chemical Society,' vol. xi. p. 464). 

Deposition of cadmium by means of a separate current. — 
According to Smee, it is difficult to obtain firm, coherent, 
deposits of this metal, from solutions of either its chloride 
or sulphate, but it may be easily deposited in a reguline 
flexible state, from a solution of theammonio-sulphnte, pre- 
pared by adding sufficient aqueous ammonia, to a solution of 
sulphate of cadmium, to re-dissolve the precipitate. 

T 



274 The Art of Electro-Metallurgy. 

A patent was taken out (March T9, 1849), by Messrs. 
Russell and Woolrich, for the electro-deposition of this metal, 
and the following is their description of the process : — 
i Take cadmium, and dissolve it in nitric acid diluted with 
five or six times its bulk of water, at a temperature of about 
8o° or ioo° Fahr., adding the dilute acid by degrees until 
the metal is all dissolved ; to this solution of cadmium, 
one of carbonate of sodium (made by dissolving one 
pound of the ordinary crystals of washing soda in one gallon 
of water) is added until the cadmium is all precipitated ; 
the precipitate thus obtained, is washed four or five times 
with tepid water ; next add as much of a solution of cyanide 
of potassium as will dissolve the precipitate ; after which 
one-tenth more of the solution of potassium salt is added 
to form free cyanide. The strength of this mixture may 
vary, but the patentees prefer a solution containing six troy 
ounces of metal to the gallon. The liquid is worked at 
about ioo° Fahr. with a plate of cadmium as an anode.' 
Very little has yet been done in the practical electro-depo- 
sition of this metal. 

M. A. Bertrand recommends, for depositing cadmium, a 
solution of its bromide, containing a little sulphuric acid ; 
also one of its sulphate ; and says the deposit obtained is 
white, adheres firmly, is very coherent, and is capable of 
receiving a fine polish (' Chemical News,' vol. xxxiv. p. 
227). 

30. Zinc. — Elec. chem. eqt. = ' -^ = 32*5. The most 

2 

common salts of zinc are the oxide, chloride, carbonate, and 
sulphate. The oxide may be formed, by precipitating a 
solution of the sulphate with aqueous ammonia, and washing 
the precipitate ; the carbonate, by precipitating such a solu- 
tion by means of washing soda. The various soluble salts, 
such as the nitrate, chloride, bromide, sulphate, acetate, &c, 
may be easily formed, by digesting, until it ceases to dissolve, 
an excess of metallic zinc, its oxide, or carbonate, with the 



Deposition of Zinc by Simple Tmmersfon. 275 

corresponding acid, diluted with water, and evaporating the 
clear solution until it crystallises. 

I have found by experiment that a solution of potassic 
cyanide will dissolve only about one half as much cyanide 
of zinc as of cyanide of copper. Zinc oxide dissolves 
somewhat freely in a boiling solution of cyanide of potassium. 
Cyanide of zinc dissolves freely in a solution of sesqui- 
carbonate of ammonium. Ferro-cyanide of zinc is but feebly 
soluble in a boiling solution, either of ferro-cyanide (yellow 
prussiate), or of ferrid-cyanide (red prussiate) of potassium, 
but dissolves freely in a boiling solution of potassic cyanide. 
Zinc deposits spread over black-leaded surfaces by the bat- 
tery process, in the same manner as copper. 

Deposition of zinc by simple immersion (see p. 79). — Zinc 
is too electro-positive a metal to be readily set free by 
the simple immersion process, except by means of metals 
more electro-positive than itself, such as magnesium. Silicon 
separates zinc from its fluoride : I heated together 1*5 grains 
of crystals of silicon, and 10*25 of perfectly dry fluoride of 
zinc, in a porcelain crucible to a red heat. Chemical action 
occurred throughout the mass, and vapour of zinc escaped ; 
some of the zinc remained in the solid state on cooling, and 
evolved bubbles of hydrogen on adding dilute hydrochloric 
acid. According to A. Cossa, aluminium separates metallic 
zinc from an alkaline solution of zinc (Watts, ' Dictionary of 
Chemistry/ vol. v. p. 54). From a solution of the sulphate, 
magnesium deposits, with energetic action, a mixture of zinc, 
the hydrated oxide, and subsulphate (Commaille, ' Chemical 
News,' vol. xiv. p. 188). From slightly acid solutions of salts 
of zinc, magnesium deposits the pure metal, and hydrogen 
gas (Roussin, 'Chemical News/ vol. xiv. p. 27). 

V. Roque coats articles of wrought and cast iron with 
zinc, in the following manner : — Mix together 1,000 measures 
of water, 550 of hydrochloric acid, fifty of sulphuric acid. 
and twenty of glycerine. Clean the iron in this mixture, 
and place it in a solution of one part of carbonate of potas- 

t 2 



2/6 The Art of Electro-Metattn rgy. 

sium and ten of water. Then immerse it during from three 
to twelve hours (according to the thickness of the coating 
required), in a mixture composed of 1,000 parts of water, ten 
of chloride of aluminium, eight of bitartrate of potassium, 
five of chloride of tin, four of chloride of zinc, and four of 
acid sulphate of aluminium (' Chemical News/ vol. xxi. p. 
288). 

Depositing zinc by contact with a second metal (see p. 83). — 
Raoult states that gold or copper in contact with zinc, in a 
concentrated and boiling solution, of chloride or sulphate of 
zinc (but not in the nitrate), acquires a metallic deposit. But 
gold in contact with iron, nickel, antimony, lead, copper, or 
silver, in cold or boiling, acid or neutral, solutions of salts 
of zinc, receives no such coating (' Chemical News/ vol. xxvi. 
p. 240; vol. xxvii. p.. 59; 'Journal of the Chemical So- 
ciety/ vol. xi. p. 464). 

Articles of copper, or brass, cleaned with hydrochloric 
acid, and immersed in contact with zinc, in a boiling saturated 
solution of salammoniac, or chloride of zinc, acquire in 
a few minutes, a specular covering of metal; but in a solution 
of cream of tartar, no such deposit occurs (R. Bottger, 
' Gmelin's Handbook of Chemistry/ vol. i. p. 501). An- 
other process is as follows : — Powdered zinc is added to a 
concentrated solution of salammoniac, and the liquid heated 
to boiling. The articles of copper or brass to be coated, are 
placed in the hot liquid in contact with zinc, and become 
covered with a brilliantly-white layer of adherent metal 
(Dr. R. Bottger, ' Chemical News/ vol. xxii. p. 108). F. Weil 
coats copper, or coppered metals, with zinc, by immersing 
them in a concentrated solution of potash or soda (heated 
to ioo° C), in contact with metallic zinc. The deposit is 
fixed and brilliant ('Chemical News/ vol. xiii. p. 2). 

Deposition of zinc by fneans of a separate current (see p. 
89). — Zinc may be deposited from its sulphate, ammonio- 
sulphate, chloride, ammonio-chloride, acetate, tartrate, &c, by 
the separate current process. As with nearly all other metals, 



Depositio?i of Zinc by a Separate Ctirrent. 27 7 

the nitrate forms a bad depositing solution. By proper man- 
agement, good coherent metal may be obtained from the 
sulphate, acetate, and chloride. A solution of zinc in 
caustic potash is not a good conductor ; a zinc anode does 
not readily dissolve in it ; similarly with the potassio-tartrate, 
and potassio-cyanide (Smee). A solution of one part of the 
sulphate in five to ten of water, with a large zinc anode, 
may be made to yield a good deposit, by a current from two 
small Smee's cells feebly charged. 

Many years ago, sheets and other articles of iron, were 
coated with zinc by electrolysis, in order to protect them 
from rusting ; but this process has been entirely superseded 
by the so-called ' galvanising,' which is not a galvanic pro- 
cess at all, but consists of dipping the previously cleaned 
iron into a bath of melted zinc ; the latter being covered 
with a layer of saline flux, in order to prevent oxidation, and 
also to dissolve any trace of oxide which may be upon the 
iron articles. Such a coating of zinc is a much more effectual 
preventive of rusting than an electro-deposited one, because 
the heat expels all moisture from the pores of the iron, and 
the layer of zinc is homogeneous and not granular or porous, 
whilst that formed by voltaic action is always more or less 
porous and very liable to contain traces of the depositing 
liquid ; the surface beneath the electro- deposit, not having 
been heated before receiving the coating, is also liable to 
contain moisture and acid, absorbed during the preparatory 
processes of cleaning, &c. 

Alexander Watt patented, in the year 1855, a process by 
means of which ' tough reguline ' zinc might be deposited. 
He first makes a mixture, composed of twenty gallons of 
distilled water, 200 ounces of cyanide of potassium, and 
eighty by measure of the strongest aqueous ammonia. He 
then fills several large porous cells, with a solution composed 
of sixteen ounces of cyanide of potassium to each gallon of 
water, and partly immerses them in the other liquid. Jn the 
porous cells, he places sheets of copper or iron to act as 



278 The A rt of Electro-Metallurgy. 

cathodes, and in the outer liquid, clean pieces of zinc to act 
as anodes, and connects the battery in the usual way, until 
about sixty ounces of zinc are dissolved, and then stops the 
current and removes the porous vessels. He next dissolves 
eighty ounces of carbonate of potassium in a part of the zinc 
solution, and returns it to the original portion, and stirs the 
mixture thoroughly. After the sediment formed has subsided, 
he decants the clear liquid for use. Articles of iron may be 
coated in this liquid. Anodes of zinc are employed, and a 
little cyanide of potassium, and liquid ammonia, are occasion- 
ally added, if necessary. The battery preferred, is composed 
of two Bunsen's cells. 

MM. Person and Sire employ a mixture composed of 
one part of oxide of zinc, dissolved in 100 of water containing 
ten of alum, at a temperature of 15 C. They use a single 
battery cell, and an anode of the same amount of surface as 
that of the articles. ' The deposition proceeds as easily as 
that of copper, and takes place indifferently on any metal — 
on platinum as well as upon copper and iron ' (' Chemical 
News,' vol. ii. p. 275). 

Estimation of zinc by means of the battery. — J. M. Merrick 
electrolysed known weights of pure double sulphate of zinc 
and ammonium, in aqueous solution, in a covered platinum 
crucible, with a platinum wire for the anode, and the crucible 
for the cathode (using a current from two or three Grove's 
cells), until all the metal was deposited ; and then weighed 
the deposit. In two analyses, i6*i6 and 16-31 per cent of 
zinc was obtained ; theory requiring 16*20 per cent. The 
deposits were washed with alcohol, and cautiously dried 
(' Chemical News,' vol. xxiv. pp. 100, 172). 

Electro-deposition of alloys of copper and zinc. — There are 
various solutions for depositing brass. As early as the year 
1841, M. de Ruolz deposited it by the battery process, from 
the mixed cyanides of zinc and copper, dissolved in a solu- 
tion of cyanide of potassium. Whenever zinc is electro- 
deposited upon perfectly clean copper, the first film deposited, 



Deposition of Brass. 279 

produces a yellow colour, by uniting with the copper. In 
accordance with this, copper articles may be superficially 
brassed, by immersing them either in a boiling solution of bi- 
tartrate of potassium, containing zinc amalgam, or in the same 
liquid, after some dilute hydrochloric acid has been added to 
it. Thicker coatings may be formed upon articles, by de- 
positing upon them, alternate thin films of zinc and copper, 
by the separate current method. Processes have also been 
patented, for coating iron and steel with brass, by depositing a 
layer of copper, and then one of zinc, upon them, and heat- 
ing them until the two metals more perfectly alloy with each 
other (see MM. Person and Sire's process, ' Chemical News,' 
vol. ii. p. 275). 

A good solution for brassing by means of a separate 
current, with an anode of brass, may be made by dissolving 
nine or ten ounces of the strongest aqueous ammonia, six- 
teen to twenty of cyanide of potassium (with or without the 
addition of twenty of the strongest aqueous hydrocyanic 
acid, 'Scheele's strength,') in 160 (i.e. one gallon) of water, 
and saturating the hot liquid with brass by means of an 
electric current ; it must be used at 2 1 2 Fahr. 

Brunei, Bisson, and Gaugain's formula, for an electro- 
brassing solution, consists of fifty parts of carbonate of potas- 
sium, two of chloride of copper, four of sulphate of zinc, and 
twenty-five of nitrate of ammonium, dissolved together in 
200 parts of cold water, and used with a brass anode, and 
a strong battery. They also give a second formula, viz. : — 
Take twelve and a half gallons of water, and dissolve in it, ten 
ounces of chloride of copper, twenty of sulphate of zinc, 
twenty-four of cyanide of potassium, and 160 of carbonate 
of potassium ; add the cyanide the last. 

Salzede's patent, dated September 30, 1847 : — To form 
the solution, take 5,000 parts of water, dissolve twelve parts 
of cyanide of potassium in 120 parts of it, then add 610 
of carbonate of potassium, forty-eight of sulphate of zinc, and 
twenty-five of chloride of copper, to the remainder of the 



2 8o The A rt of Electro-Metallurgy. 

water, and heat the mixture from 144° to 172 Fahr. ; and 
when the salts are entirely dissolved, add 305 parts of nitrate 
of ammonium, allow the liquid to remain undisturbed for 
twenty hours, and then add the solution of cyanide of potas- 
sium j allow it to remain again till clear, and then draw off 
the transparent liquid, which is ready for use ; work the solu- 
tion with a large brass anode and a strong battery. Another 
liquid which he uses for brassing, consists of 5,000 parts of 
water, 500 of carbonate of potassium, thirty-five of sulphate 
of zinc, fifteen of chloride of copper, and fifty of cyanide 
of potassium. 

Russell and Woolrich's patent, dated March 19, 1849 : — 
Take ten pounds of acetate of copper, one of acetate of zinc, 
ten of acetate of potassium, and five gallons of hot water; 
dissolve the salts in the water, add as much of a solution of 
cyanide of potassium as will precipitate the mixture and just 
re-dissolve the precipitate ; and then add about one-tenth 
more of the cyanide. Use a brass anode, or else two anodes, 
one of zinc and one of copper. 

Joseph Steele's patent, dated August 9, 1850 : — Dissolve 
two and a quarter pounds of American potash in six gallons 
of hot water, and filter the solution ; also dissolve two and a 
half ounces of acetate of copper in half a pint of strong 
liquid ammonia, and add it to the first liquid, with stirring ; 
then add four or five ounces of sulphate of zinc, and stir till 
dissolved ; and finally add two ounces of cyanide of potas- 
sium ; filter the resulting solution, and use it at ioo° Fahr., 
with a brass anode. To obtain a dark-coloured brass, add 
more acetate of copper ; and to obtain it of a lighter colour, 
add more sulphate of zinc. 

Mr. Wood's solution is composed thus: — Dissolve one 
pound (troy weight) of cyanide of potassium, two ounces of 
cyanide of copper, and one of cyanide of zinc, in one gallon 
of distilled water, and add two ounces of salammoniac. 
For coating smooth articles, use the solution at 160 Fahr. 



Deposition of Brass. 281 

with a battery of from three to twelve Grove's cells. It is 
suitable for coating iron (' Scientific American '). 

Mr. Watt gives the following formula for a brassing liquid : 
—Acetate of copper five parts, cyanide of potassium eight, 
sulphate of zinc ten, liquid ammonia forty, and caustic potash 
seventy-two parts. Reduce the copper salt to powder, and 
dissolve it in eighty parts of water ; then add twenty of 
the aqueous ammonia. Dissolve the zinc salt in 160 parts 
of water at 180 Fahr., add the remaining twenty of 
ammonia to it, and stir the mixture strongly. Dissolve 
the potash in 160 parts of water, and the cyanide in 160 
of hot water. Add the solution of copper to that of zinc, 
then add the caustic potash, and then the cyanide. Dilute 
the mixture to eight gallons by addition of water, and 
thoroughly stir the solution. Use a strong battery, add a 
little ammonia occasionally, and when it works slowly, add 
cyanide. Keep the brass anode clean. 

According to Dr. Heeren, a brassing solution may be 
formed, by taking a mixture containing a great excess of 
zinc and very little copper, thus : — Dissolve one part of 
sulphate of copper, eight of sulphate of zinc, and eighteen 
of cyanide of potassium, in separate portions of warm water. 
Mix the copper and zinc solutions, then add the dissolved 
cyanide and a further quantity of 250 parts of distilled water, 
and stir the mixture. The bath is used at a boiling tempera- 
ture, with a current from two Bunsen's cells. Very rapid 
deposits of brass have been thus obtained upon articles of 
copper, zinc, brass, and Britannia-metal ('The Chemist,' 
No. 16, January 1855, New Series, p. 342). 

Morris and Johnson's patent, dated December 11, 1852. 
According to this, dissolve one pound of cyanide of potas- 
sium, one of commercial carbonate of ammonium, two ounces 
of cyanide of copper, and one of cyanide of zinc, in a 
gallon of water, and use the solution at 150 Fahr. with a 
large anode of brass and a powerful battery. Or a solution 



282 The A rt of Electro-Metallurgy. 

may be taken of one pound of cyanide of potassium, and 
one of carbonate of ammonium, dissolved in one gallon of 
water, and saturated with copper and zinc to the requisite 
degree by means of a strong current, a large brass anode and 
a small cathode, until the latter receives a good deposit of 
brass, the liquid being at a temperature of 150 Fahr. To 
increase the proportion of copper in the deposit, either add 
cyanide of potassium, or raise the temperature of the liquid ; 
and to increase that of zinc, either add carbonate of am- 
monium, or lower the temperature. 

Roseleur gives the following recipes for making brassing 
solutions. No. 1. — Dissolve in 1,000 parts of water, twenty- 
five of sulphate ot copper, and twenty-five to thirty of sul- 
phate of zinc ; or twelve and a half of acetate of copper, and 
twelve and a half to fifteen of fused chloride of zinc. Pre- 
cipitate the mixture, by means of 100 parts of carbonate of 
sodium dissolved in plenty of water, and stir the mixture. 
Wash the precipitate several times by adding water to it, 
stirring, allowing the precipitate to subside, and pouring the 
clear liquid away. Add to the washed precipitate, a solution 
composed of fifty parts of bisulphite of sodium, and too 
of carbonate of sodium, dissolved in 1,000 of water, and, 
whilst stirring with a wooden rod, add a strong solution of 
ordinary cyanide of potassium, until the precipitate is just 
all re-dissolved. Then add two and a half or three parts of 
free cyanide. No. 2. — To form a cold bath for brassing 
ali metals, dissolve in 200 parts of water, fifteen of cupric 
sulphate, and fifteen of sulphate of zinc, and then add a solu- 
tion of forty parts of carbonate of sodium dissolved in too of 
water, and stir the mixture. Allow the precipitate to subside, 
throw away the clear liquid, and wash the sediment by addi- 
tion of water, followed by subsidence, and decantation. Add 
to the drained and wet precipitate, 900 parts of water, con- 
taining twenty of bisulphite and twenty of carbonate of 
sodium dissolved in it. Dissolve twenty parts of cyanide 
of potassium, and two-tenths of a part of arsenious acid 



Deposition of Brass upon Iron. 283 

(white arsenic), in 100 of water, and add it to the previous 
liquid ; this decolourises the mixture, and completes the 
brassing solution. The arsenious acid causes the deposit to 
be bright, but if added in too large a quantity, whitens it ; 
this latter effect, however, soon disappears by working the 
liquid. In using this bath, if the deposit is dull, add a little 
of the arsenic ; if it looks earthy or ochreous, add cyanide ; 
if too red, add zinc salt, and if necessary also cyanide ; if 
too white, add copper and cyanide ; if its action is very 
slow, add copper and zinc salts, and if necessary also cyanide. 
As the brass is deposited faster than it dissolves, salts of 
copper, and of zinc, with cyanide, must be added occasion- 
ally. When by addition of these substances, the specific 
gravity of the solution becomes greater than 1*091, the solu- 
tion must be diluted with water to a sp. gr. not below ro36. 
No. 3. — For coating steel, cast iron, wrought iron, and 
tin : — Dissolve two parts of bisulphite of sodium, five of 
cyanide of potassium (of 75 per cent), and ten of carbonate 
of sodium, in eighty of distilled water ; and add to the mix- 
ture, one part of fused chloride of zinc, and one and a quarter 
parts of acetate of copper, dissolved in twenty of water. 
No. 4. — For coating articles of zinc : — Dissolve twenty 
parts of bisulphite of sodium, and 100 of cyanide of potas- 
sium (of 75 per cent), in 2,000 of water ; and dissolve 
thirty-five parts of chloride of zinc, thirty-five of acetate of 
copper, and forty of aqueous ammonia, in 500 of water; 
mix the two solutions, and filter the mixture. Too strong a 
current in these solutions usually makes the deposit white, 
and too weak a one, or keeping the articles in motion, 
makes it red. The proportion of zinc in the baths may be 
increased by using a zinc anode, and of copper by employ- 
ing a copper one. The brass anodes may be kept free fr< >m 
undissolved oxide of zinc, by adding the minimum quantity 
of ammonia; but that must not be added to cold solu- 
tions used for brassing iron. To preserve the colour of the 
deposit, rinse the coated articles in water, then in water 



284 The A rt of Electro-Metallurgy. 

made slightly alkaline by addition of caustic lime, and then 
thoroughly dry them in a stove. 

For coating cast iron with brass, Walenn recommends a 
bath, composed of an aqueous solution of equal parts of 
ammonic-tartrate and potassic-cyanide. After addition of 
cyanide of copper, and cyanide of zinc, in certain propor- | 
tions, the oxides of the metals are added to the solution. I 
If upon trial, hydrogen is evolved at the cathode, a little 
ammoniuret of copper is added to the cold bath. The j 
temperature at which this liquid is used, determines the colour ' 
of the brass, and may vary from 6o° C. to nearly the boiling ! 
point (' Chemical News,' vol. xxi. p. 273). He also makes 
the following remarks on the electro-deposition of copper 
and brass. ' A solution containing one pound of cupric 
sulphate, and one of sulphuric acid, to a gallon of water, j 
deposits the metal in a solid compact mass, with a somewhat 
botryoidal surface. The addition of one ounce of zinc sul- 
phate (as recommended by Napier) prevents this botryoidal 
form, and renders the deposit tough, compact, and even, j 
From a solution containing a greater proportion of zinc I 
sulphate, the copper is deposited in tufts of needles standing > 
at right angles to the surface of the metal. Ordinary electro- | 
brassing liquids show the same peculiarity in even a more 
marked degree, and this makes it impossible to produce a , 
good deposit of more than *oi to -03 inch in thickness. This 1 
form of deposit is owing chiefly to a copious evolution of 
hydrogen taking place during its formation.' Flowever the ! 
author has found, that by employing a solution containing both j 
the oxides and the cyanides of the two metals, together with | 
some neutral tartrate of ammonium, this evolution of hydro- 
gen may usually be avoided, or, should it, nevertheless, take 
place to a slight extent, it may be entirely stopped by the 
addition of some cupric ammonide. Such a solution yields ! 
brass of a uniform character, and the deposit, which may be 
obtained of any desired thickness, is tough, and has a com- 1 
pact, even texture. As there is no evolution of hydrogen, 1 



Deposition of German- Silver. 2S5 

no electric force is wasted, and perfect results may be ob- 
tained with a single Wollaston's or Sniee's cell ; but in prac- 
tice a little stronger current than this is employed, in order 
to hasten the process (' Philosophical Magazine,' 4th Series, 
vol. xli. p. 41; 'Chemical News,' vol. xxii. pp. 1, 181; 
4 Journal of the Chemical Society,' vol. x. p. 103). 

Deposition of other alloys of zinc. — Watt states that he has 
1 succeeded in depositing an alloy of copDer, zinc, and nickel, 
forming a very good quality of german-silver, by dissolving 
german-silver in nitric acid, precipitating with an alkali, and 
re-dissolving with cyanide of potassium ' (' Electro-Metal- 
lurgy,' by A. Watt ; Weale's ' Elementary Series,' p. 91). 

Newton patented (July 29, 1850) a solution for depositing 
an alloy of copper, tin, and zinc ; it consisted of the double 
cyanide of copper and potassium, in combination with 
' zincate ' and stannate of potassium, ' or the double tartrates 
of the metals and potassium, may be used.' 

Messrs. Morris and Johnson (according to their patent), 
deposit german-silver by the following process : — Dissolve 
one pound of cyanide of potassium, and one of carbon- 
ate of ammonium, in a gallon of water, heat the solution 
to 150 Fahr., immerse a large anode of german-silver in the 
liquid, and a small cathode of any suitable metal, connect 
the two with a powerful battery, and pass the current of 
electricity until a considerable amount of metal is dissolved, 
and a bright cathode receives a deposit of good colour ; the 
solution is then ready for use. If the deposit becomes too 
red, add carbonate of ammonium ; if too white, add cyanide. 

Separation of copper and zinc by electro-deposition. — Ac- 
cording to M. Hautefeuille, the oxides of copper and zinc, 
dissolved in aqueous ammonia, may be separated by the 
following process : — Add an excess of acetic acid to the 
solution, immerse a clean sheet of lead, and boil the mixture- 
two hours, or until it becomes quite colourless ; the whole of 
the copper is then precipitated in the metallic state (' The 
Chemist,' New Series, part xviii., March 1855, p. 334). 



2 S6 The A rt of Electro-Metallurgy. 



CLASS V. EARTH AND ALKALINE EARTH 
METALS. 

MAGNESIUM — CERIUM — LANTHANUM — DIDYMIUM — GALLIUM 
— ALUMINIUM — GLUCINIUM — CALCIUM — STRONTIUM — 
BARIUM. 

31. Magnesium. — Elec-chem. eqt.=^^-=i2'i5. The 

ordinary salts of this metal are the oxide (calcined magnesia), 
the nitrate, chloride, carbonate, and sulphate; the most fre- 
quent impurity in them is lime. As the metallic magne- 
sium of commerce is free from calcium, and very pure, extra 
pure salts of the metal may be made by means of it. The 
nitrate, chloride, and sulphate, may be made by saturating 
the corresponding diluted acids, with the metal, the oxide, 
or carbonate, and evaporating the solutions. In evaporating 
a solution of the chloride to dryness, towards the end of the 
operation, some of the salt is decomposed by the watery 
vapour, hydrochloric acid being formed, and oxide of mag- 
nesium left ; and to obviate this, a portion of salammoniac 
is added when the solution has become very concentrated. 

Magnesium is highly electro-positive ; it precipitates as 
metal, from solutions of their salts, bismuth, platinum, gold, 
silver, mercury, copper, lead, thallium, tin, and cadmium 
(Roussin, 'Chemical News,' vol. xiv. p. 27). According to 
Phipson, magnesium deposits nearly all metals from their 
neutral solutions (even iron and manganese from ferrous and 
manganous salts) in the metallic state. It deposits platinum, 
gold, silver, bismuth, mercury, copper, nickel, cobalt, iron, 
lead, thallium, tin, cadmium, and zinc, but not aluminium 
(Watts, ' Dictionary of Chemistry,' vol. v. p. 795). 

I melted to a perfect liquid, at nearly a white heat, a 
mixture of six grains of magnesic fluoride, and four of calcic 
fluoride; then added two grains of crystals of silicon, the 



Deposition of Magnesium. 



287 



crystals were not dissolved, and there appeared no signs of 
metallic magnesium having been separated. 

Electrolysis of salts of magnesium. — When moistened 
sulphate of magnesium is formed into a cup upon a platinum 
plate, the cup filled with mercury and made the cathode, 
and the platinum the anode, with a current from a powerful 
battery, magnesium is deposited into the mercury. 

Bunsen electrolysed fused chloride of magnesium, at a red 
heat, in a deep and covered porcelain crucible, divided by a 
vertical partition of porous porcelain, which extended half- 
way down the vessel. The electrodes were of carbon, an 1 in- 
troduced through openings in the cover ; and the current was 
from ten cells of a zinc and carbon battery. As magnesium 
is a light metal, it would rise to the surface of the mixture 
and burn in the air ; and, in order to prevent this as much 
as possible, the cathode was notched (see fig. 28), so that 
the melted metal collected in the notches. According to 
Matthiessen, a fused mixture, in the proportions of four 



Fig. 28. 





molecules of magnesic, and three of potassic chloride, forms 
a much better electrolyte, because the magnesium sinks in 
it. 'A solution of the chloride of sodium or ammonium, 
electrolysed with electrodes of magnesium wire, deposits a 
black powder of suboxide of magnesium upon the anodes 
(W. Beetz, < Watts' Chemical Dictionary,' Supplement, p. 796) 



288 The A rt of Electro-Metallurgy. 

According to M. A. Bertrand, a strong current deposits 
magnesium in a few minutes upon a sheet of copper, in an 
aqueous solution of the double chloride of magnesium and 
ammonium. The deposit is homogeneous, strongly adherent, 
and polishes readily (' Chemical News,' vol. xxxiv. p. 227). 

32. Cerium, lanthanum, and didymium. — To deposit 
either of these metals, its chloride is mixed with salammoniac 
(both as dry as possible), and the mixture heated to redness in 
a platinum crucible to expel all the salammoniac. A porous 
clay vessel, of the best quality, is filled with the residue, then 
placed in a Hessian crucible, surrounded by a cylinder of 
sheet iron (with a long projecting strip for connexion), to 
serve as the anode, and the space between the two vessels 
filled with a previously melted mixture of an equal number 
of equivalents of the chlorides of potassium and sodium. 
A thick iron wire, enclosed in a clay pipe, has a coil of very 
fine iron wire at its extremity to serve as the cathode, and is 
immersed in the fused salt in the inner vessel. The fusion 
is effected by preference in a fire of glowing charcoal, to 
prevent as far as possible the presence of aqueous vapour, 
and a strong current is employed (Bunsen, ' Electrical News,' 
vol. i. p. 184). 

33. Gallium. — Gallium is allied to aluminium. It melts 
easily (at 29*5° C), when held between one's fingers ; but 
does not easily volatilise or oxidise, even when heated to 
bright redness. Liquid gallium is whiter than mercury ; the 
solid metal is hard, and somewhat malleable, of specific 
gravity 47, not oxidised by cold nitric acid, but dissolves in 
cold dilute hydrochloric or hot nitric acid The oxide of 
this metal is not very soluble in aqueous ammonia, but a 
solution of caustic potash dissolves a large quantity of it. 
The metal has been obtained by the electrolysis of both these 
solutions, formed by adding an excess of those alkalies to 
the sulphate of gallium. It is deposited upon the platinum 
cathode as a dead, whitish- grey coating, formed of minute 
globules like mercury (' Chemical News,' vol. xxxiii. p. 193). 



Deposition of Aluminium. 2S9 

34. Aluminium.— Elec. chem. eqt. = 2 -l$-= 9-16. The 

3 
oxide (alumina), chloride, sulphate, alumand (a double sul- 
phate of aluminium and an alkaline metal, usually ammo- 
nium, or potassium) are its most common salts ; the chloride 
sulphate, and alum, are freely soluble in water. 

Magnesium does not deposit aluminium as metal from 
its solutions (Roussin, ' Chemical News,' vol. xiv. p. 27). 

Electrolysis of salts of aluminium. — With regard to the 
separation of aluminium by means of electrolysis, M. H. 
Sainte-Claire Deville says: — 'It appeared to me impossible 
to obtain aluminium by the battery m aqueous liquids. I 
should believe this to be an impossibility, if the brilliant ex- 
periments of M. Bunsen on the production of barium, did 
n J bt shake my conviction. Still I may say, that all processes 
of this description which have recently been published for the 
preparation of aluminium, have failed to give me good results. 
It is of the double chloride of aluminium and sodium, of 
which I have already spoken, that this decomposition is 
effected. The bath is composed of two parts, by weight, of 
chloride of aluminium, with the addition of one part of dry 
and pulverised common salt. The whole is mixed in a 
porcelain crucible, heated to about 392 Fahr. The com- 
bination is effected with disengagement of heat, and a liquid 
is obtained which is very fluid at 39 2 Fahr., and fixes at 
that temperature. It is introduced into a vessel of glazed 
porcelain, which is to be kept at a temperature of about 
392 Fahr. The cathode is a plate of platinum, on which 
the aluminium (mixed with common salt) is deposited in 
the form of a greyish crust. The anode is formed of a 
cylinder of charcoal, placed in a perfectly dry, porous 
vessel, containing melted chloride of aluminium and sodium. 
(The densest charcoal rapidly disintegrates in the bath, and 
becomes pulverulent, hence the necessity of the porous 
vessel.) The chlorine is thus removed, with a little chloride 
of aluminium proceeding from the decomposition of the 

u 



290 The Art of Electro-Metallurgy. 

double salt. This chloride would volatilise and be entirely 
lost, if some common salt were not in the porous vessel. ' 
The double chloride becomes fixed, and the vapours cease. 
A small number of voltaic elements (two are all that are ab- ; 
solutely necessary) will suffice for the decomposition of the j 
double chloride, which presents but little resistance to the j 
electricity. The platinum plate is removed when it is suffi- j 
ciently charged with the metallic deposit. It is suffered to ! 
cool, the saline mass is rapidly broken off, and the plate re- ! 
placed' ('The Chemist,' New Series, No, 13, October I 
1854, p. 12). 

M. Duvivier states, that by passing an electric current J 
from eighty Bunsen's cells, through a small piece of ' laminae 
disthene ' between two carbon points, the disthene melted 
entirely after two or three minutes ; the elements which 
composed it, were partly disunited by the power of the 
electric current, and the aluminium freed from its oxygen. 
Several globules of the metal separated, one of which was 
as white and as hard as silver (' The Chemist,' New Series, 
No. xi., August 1854, p. 687). 

Bunsen electrolysed fused chloride of aluminium and 
sodium, by a similar process to that already described in de- 
positing magnesium (see p. 287). The salt fused at 356°C, 
and readily yielded the metal. The temperature of the liquid 
should be raised nearly to the melting-point of silver ; the 
particles of liberated aluminium then fuse, unite together, 
and form globules, which, being of greater specific gravity 
than the salt, fall to the bottom of the crucible. I electro- 1 
lysed a strong solution of pure fluoride of aluminium, con- 
taining free hydrofluoric acid, using the platinum containing 
vessel as the cathode, and a sheet of platinum as the anode ; 
gas was evolved freely from the latter, and the liquid became 
heated. 

M. Corbelli, of Florence, deposits aluminium, by electro- 
lysing a mixture of rock-alum, or sulphate of aluminium, and 
the chlorides of calcium or of sodium, the anode being 



Deposition of Aluminium. 291 

formed of iron wire, coated with an insulating material, and 
dipping into mercury placed at the bottom of the solution ; 
and the cathode of zinc immersed in the solution. Alu- 
minium is then deposited upon the zinc, and the chlorine 
which is eliminated at the anode, unites with the mercury, 
and forms calomel (Watts, ' Dictionary of Chemistry,' vol. i. 
p. 152). 

Thomas and Tilley took out a patent Dec. 26, 1854, for 
depositing aluminium from a solution, composed of freshly 
precipitated alumina, dissolved in boiling water containing 
cyanide of potassium; and another, Dec. 6, 1855, for de- 
positing it from a solution of calcined alum in aqueous 
cyanide of potassium ; also from several other liquids ; and 
for depositing alloys of aluminium and silver; aluminium, 
silver, and copper ; aluminium and tin ; aluminium, silver, 
and tin ; aluminium and copper ; aluminium and nickel ; 
aluminium and iron, &c. 

J. B. Thompson states, that he has for more than two 
years, been depositing aluminium on iron, steel, and other 
metals, at a temperature of about 500 Fahr., and also de- 
positing aluminium bronze of various tints, from the palest 
yellow to the richest gold colour (' Chemical News,' vol. 
xxiv. p. 194). 

Jeancon patented a process, for depositing aluminium 
from an aqueous solution of a double salt of that metal and 
potassium, of sp. gr. 1-161, by means of a current from three 
Bunsen's cells, the solution being at 140 Fahr. (' Telegraphic 
Journal,' vol. i. p. 308). T. Bell also patented a process, for 
depositing aluminium upon other metals, from the double 
chloride of that metal and potassium ('Chemical News.' 
vol. v. p. 153). M. A. Bertrand states, that he has deposited 
aluminium upon a plate of copper, in a solution of the 
double chloride of aluminium and ammonium, by employ- 
ing a strong current ; and that the deposit was capable of 
receiving a brilliant polish (' Chemical News, vol. xxxiv. p. 
227). 

u 2 



292 The A rt of Electro-Metallurgy. 

According to C. Winckler, plating with aluminium can- 
not be effected by electro-deposition (' Chemical News,' vol. 
xxvi. p. 157; 'Journal of the Chemical Society,' vol. x. 
p. 1 134). Sprague also states his inability to deposit 
that metal (Sprague, ' Electricity,' p. 309).. 

Aluminium used as an anode in electrolysing dilute sul 
phuric acid, stops the current ; but not if it is employed as 
the cathode (' Telegraphic Journal,' vol. iii. p. 59 ; ' Chemi- 
cal News/ vol. xxxi. p. 99). 

35. Glucinium— Elec.-chem.' eqt. =.2-3_= 4*65. The 

commonest salts of this metal, are the carbonate and sul- 
phate ; the latter is freely soluble in water ; the nitrate and 
chloride are also very soluble, and may be easily made, by 
adding sufficient of the carbonate to the respective acids, 
and evaporating the solutions. 

Becquerel deposited the pure metal from a concentrated 
solution of its chloride (by means of a current from twenty 
cells), in the form of brilliant, steel-grey, crystalline laminse 
(Gm din's - Handbook of Chemistry/ vol. iii. p. 293). 

36. Calcium. — Elec.-chem. eqt. = — = 20. The com- 
mon salts of calcium, are the oxide (caustic lime), the nitrate, 
fluoride, chloride, bromide, carbonate (chalk or whiting), 
sulphate, phosphate, &c. Ordinary caustic lime is often im- 
pure ; a much purer kind may be obtained, by heating the 
pure carbonate to full redness ; the latter may be obtained 
as follows : Add an excess of clear lime-water to a solu- 
tion of nitrate of calcium ; filter the liquid, and precipitate 
it with a mixture of ammonia and carbonate of ammonium, 
dissolved in water, and wash the precipitate thoroughly. 
Pure soluble salts of lime may be obtained, by neutralising 
the respective pure acids with the pure carbonate, and eva- 
porating the clear solutions. The sulphate of calcium is only 
sparingly soluble in water, the fluoride and phosphate much 
less so ; caustic lime also does not dissolve very freely. 



Deposition of Calcium. 293 

Electrolysis of salts of calcium. — Sir H. Davy first depo- 
sited impure calcium by electrolysis into a cathode of mer- 
cury during the year 1808 ; and since that period, several 
other investigators have effected the same object, by means 
of much less powerful electric currents. 

M. Fremy fused pure fluoride of calcium in a platinum 
crucible, and electrolysed it ; a brisk effervescence occurred 
in the mass, and a gas was evolved at the positive pole, which 
corroded glass ; metallic calcium was deposited upon the 
cathode, and was at once converted into lime by the atmo- 
sphere. It was difficult to make the observations, and the 
crucible was soon alloyed, and leaked, and the melted fluo- 
ride escaped (' The Chemist,' New Series, vol. ii. p. 548). 

Matthiessen melted and electrolysed a mixture, in tht 
proportions of two molecules of chloride of calcium, and one 
of chloride of strontium, with a small quantity of sal ammo- 
niac, in a porcelain crucible, with an anode of gas-carbon, 
and a cathode formed by winding a thin iron wire round a 
thicker one, and dipping it only just into the fused mixture. 
The calcium was deposited in beads upon the fine wire. 

Bunsen electro-deposited metallic calcium, in a similar 
manner to that employed for manganese and chromium 
(see pp. 250, 253), except that the density of the current 
employed was greater. He acidulated a concentrated and 
boiling hot solution of the chloride, with hydrochloric acid, 
poured the boiling liquid into the porous cell, and employed 
as a cathode, an amalgamated platinum wire. The calcium 
was deposited as a grey layer upon the amalgamated surface. 
The process is difficult, because the calcium quickly oxidizes 
to a layer of lime, which covers the cathode, and stops the 
current. The deposit must be frequently removed, and the 
wire freshly amalgamated, each time before re-immersi- in . 
and even then but a small amount of the metal is obtained 
(' The Chemist,' New Series, vol. i. part ii., August 1S54, 
p. 686). 

Herschel observed, that in a solution of chloride of cal- 



294 The Art of Electro -Metallurgy. 

cium undergoing electrolysis, the cathode evolved gas, and 
became covered with caustic hydrate of lime. 

37. Strontium. — Elec.-chem. eqt.= — IS = 4375. The 

ordinary salts of strontium, are the nitrate, chloride, carbo- 
nate, and sulphate ; the two former are freely soluble in 
water, and the two latter insoluble. 

Silicon does not separate strontium from its fluoride. I 
heated to redness, a mixture of crystals of silicon and fluo- 
ride of strontium ; the crystals suffered no loss of weight, 
did not appear corroded, and no signs of free strontium 
were obtained. 

Electrolysis of salts of strontium. — Sir H. Davy first de- 
posited this metal by electrolysis, in the year 1808, by forming 
into a cup, a pasty mass of its carbonate with water, and 
placing it upon a platinum dish as an anode, the cup being 
filled with mercury to act as the cathode. On passing a 
current from a 500-cell battery through it, the strontium was 
deposited upon, and absorbed by, the mercury. 

Bunsen obtained strontium, in a precisely similar way to 
that of obtaining calcium (p. 293), using a salt of strontium 
instead of one of that metal (Watts, ' Dictionary of Chem- 
istry/ vol. ii. p. 437). Matthiessen obtained it from the 
fused chloride in the following manner : — A small porous 
cell was placed in a porcelain crucible, and both vessels 
nearly filled with anhydrous chloride of strontium, the level 
of that in the porous cell being the highest. The salt was 
melted so that a crust appeared on its surface. The cathode 
consisted of a thick iron wire, enclosed in the stem of a 
tobacco-pipe, so that only -^th of an inch of it projected at 
the lower end, round which a very thin iron wire was coiled. 
The anode was a cylinder of sheet iron placed in the outer 
space. The cathode was immersed in the inner vessel, and 
the current passed ; the metal collected upon it beneath the 
crust (Watts, ' Dictionary of Chemistry,' vol. ii. p. 438). 

Strontium is electro-negative to potassium and sodium in 
water, but positive to magnesium. 



Deposition of Bar item. 295 

38. Barium. — Elect.-chem. eqt. = HZ = 68-5. Its or- 

2 

dinary salts are, the oxide, hydrated oxide (both termed 
caustic baryta), nitrate, chloride, carbonate, and sulphate. 
The oxide, nitrate, and chloride are soluble in water ; the 
carbonate and sulphate are insoluble. 

Crookes deposited barium, by simple immersion of an 
alloy of sodium and mercury in a saturated solution of 
barium chloride at 93 C. The deposited metal dissolved 
in the mercury, and formed an amalgam ('Chemical News,' 
vol. vi. p. 194; Watts, 'Dictionary of Chemistry,' vol. v. 
p. 252). 

Electrolysis of salts of barium. — Davy first deposited 
barium, by passing a powerful electric current through a 
concentrated solution of hydrate of baryta, into a cathode of 
mercury ; the deposit formed an amalgam with that metal. 

Bunsen obtained barium, by electrolysis of a boiling hot, 
concentrated, and acidulated solution of its chloride, in a 
similar manner to that of separating calcium (see p. 293) ; it 
was more easily obtained. The deposit upon the mercurial 
surface formed an amalgam, which was silvery-white, and 
very crystalline ('The Chemist/ New Series, vol. i. p. 686 ; 
Watts, 6 Dictionary of Chemistry,' vol. i. p. 500). 

Matthiessen obtained barium from its chloride, in a 
similar manner to that in which he deposited strontium (see 
p. 294). 

A solution of nitrate of barium, electrolysed by means of 
platinum electrodes, yields nitric acid at the anode, and baryta 
at the cathode (Sir H. Davy). 

CLASS VI. ALKALI-METALS. 

LITHIUM — SODIUM — POTASSIUM — RUBIDIUM — CESIUM — 

AMMONIUM. 

39. Lithium. — Elec.-chem. eqt. = 7. The most common 
salt of lithium, is the carbonate, and from this the other salts 



296 The A rt of Electro-Metallurgy. 

may be easily prepared, by adding an excess of it to the par- 
ticular acid, filtering the mixture, and crystallising the solu- 
tion. All the salts of lithium (except the phosphate), formed 
by adding the carbonate to the common mineral acids, are 
freely soluble in water. 

I added crystals of silicon to a fused mixture of the fluo- 
rides of lithium and sodium, but the silicon was not corroded 
or diminished in weight, and lithium was not deposited. 

Electrolysis of salts of lithium. — Bunsen was the first 
person who electro-deposited this metal (Watts, ' Dictionary 
of Chemistry,' vol. hi. p. 727). By electrolysing fused chlo- 
ride of lithium, with a current from four or six Bunsen's 
cells, an anode of gas-coke, and a cathode of iron wire, he de- 
posited silver- white metal upon the wire (Watts' ' Dictionary 
of Chemistry,' vol. ii. p. 437, and vol. in. p. 727). Schnitzler 
also electrolysed a mixture of the fused chlorides of lithium 
and ammonium, with a current from twelve Bunsen's cells, 
and a cathode of iron wire ('Journal of the 
Chemical Society,' vol. xii. p. 961). 

I fused some fluoride of lithium in an 
open platinum crucible, within a partially 
covered clay muffle (see fig. 29), and electro- 
lysed it by means of a current from six 
Smee's elements, and two flat platinum wire 
helices as electrodes, during thirty minutes. 
The conduction was free, and much gas was 
evolved from the anode only, all the time. The anode was 
not corroded; a small amount of lithium was deposited upon 
the platinum cathode, and allojed with it. By electrolysing 
a larger mass of the salt with a current from six Grove's cells 
and a thick platinum wire cathode, enclosed within, but in- 
sulated from, a platinum tube, to exclude the air from contact 
with the deposited lithium, the action was copious ; with a 
gold anode, the gold was corroded freely, and particles of it 
in large quantity, floated in the liquid and united the elec- 
trodes. The cathode swelled greatly, and its lower end, 




Deposition of Sodium. 207 

bent itself towards the anode, became quite grey in colour, 
and split in the direction of its length. 

40. Sodium. — Elec.-chem. eqt. = 23. Nearly all the 
common salts of sodium are freely soluble in water, and may 
be readily obtained in a pure state, by neutralising the pure 
acids with pure carbonate of sodium, and evaporating the 
solutions. The fluoride is one of the least soluble. 

Soon after Sir H. Davy first isolated sodium, Gay-Lussac 
and Thenard showed, that iron at a white heat, set free the 
metal from caustic soda. Other investigators soon found 
that carbon acted similarly. I have also observed that 
crystals of silicon, thrown into melted fluoride of sodium, 
evolved small bubbles of vapour, which exploded and burned 
with a yellow flame, on arriving at the surface of the liquid. 
In a second experiment, seven grains of the dry fluoride in 
powder, and one grain of the crystals, were mixed, and heated 
to redness ; the silicon lost "15 of a grain in weight. 

Electrolysis of salts of sodium. — Sir H. Davy first electro- 
deposited sodium in the year 1807, by moistening its hydrate 
with water in a platinum capsule, which acted as the anode, 
dipping a platinum wire cathode in the salt, and using a 
current from a battery composed of 100 to 200 cells. He also 
deposited it more easily into mercury, in a similar way to that 
already described under magnesium (see p. 287), and thus 
obtained an amalgam of the two metals. 

According to Faraday, fused borax is decomposed by 
electrolysis into oxygen and sodium, and the latter takes 
oxygen from the boracic acid and sets free boron (see p. 46). 
According to Burckhard, ' Carbonate of sodium in a fused 
state is a good conductor ; by electrolysis it is decomposed 
into carbonic acid and soda, but a small portion of carbon 
is also set free.' He also states, that fused pyrophosphate of 
sodium, electrolysed with platinum electrodes, yields phos- 
phide of platinum, but the chief result is, that the salt splits 
up into oxygen, phosphorus, and soda ('Chemical News/ 
vol. xxi. p. 238). In the electrolysis of melted sulphate of 



298 The A rt of Electro-Metallurgy. 

sodium with platinum electrodes, sodium is deposited, and 
combines with the cathode (Brester, ' Chemical News,' vol. 
xviii. p. 145). A fused mixture of the chlorides of calcium 
and of sodium, yields a deposit of the latter metal, when 
electrolysed in a certain manner (Matthiessen, Watts, ' Dic- 
tionary of Chemistry,' vol. i. p. 715). 

By electrolysing a solution of common salt, Higgins and 
Draper observed, that chlorine was set free at the anode, and 
hydrogen gas and soda at the cathode ; but if the cathode 
consisted of mercury, sodium amalgam was produced. 

Hisinger and Berzelius, electrolysed a solution of com- 
mon salt, with silver electrodes ; gas was evolved at the 
cathode, and after a time at the anode also ; the anode be- 
came covered with argentic chloride, the liquid near it con- 
tained dissolved chlorine, and the solution near the cathode 
contained free soda ; with lead electrodes, the negative wire 
evolved gas, and received a deposit of crystals of lead, and 
the anode became coated with plumbic chloride. 

I electrolysed a saturated aqueous solution of sodic 
fluoride, by a current from six Grove's cells, with platinum 
electrodes ; gas was evolved from the anode, and emitted 
an odour of ozone powerfully. From the electrolysis of sul- 
phide of sodium, Buff concluded, that the sodium travelled 
towards the cathode, and all the sulphur to the anode, 
(' Chemical News,' vol. xv. p. 279). A solution of ordinary 
phosphate of sodium, is resolved by electrolysis, into soda at 
the cathode, and phosphoric acid at the anode. 

41. Potassium. — Elec.-chem. eqt. = 39-1. As the salts 
of potassium, like those of sodium, are very numerous, and 
are rarely electrolysed for the purpose of depositing their 
metal, I need only remark, that most of them may be prepared 
in a pure state, by neutralising the respective acids by pure 
potassic carbonate ; and that nearly the whole of them are 
freely soluble in water ; and I must refer the reader to a 
work on chemistry for special chemical information respecting 
them. 



Deposition of Potassium. 299 

Soon after Sir H. Davy first isolated potassium by elec- 
trolysis, Gay-Lussac and Thenard showed, that the metal was 
also set free by the contact of iron with melted potash at a 
white heat. Other investigators found subsequently, that 
carbon acted similarly. According to H. St. -Claire Deville, 
even silver deposits potassium, when immersed in fused 
potassic iodide ; it also renders an aqueous solution of iodide 
of potassium alkaline, and forms argentic iodide, by a simi- 
lar reaction ('The Chemist,' New Series, vol. iv. p. 329). 

Electrolysis of salts of potassium.— -Sir H. Davy first 
deposited this metal in the year 1807, by the influence of an 
electric current upon wet hydrate of potash, in a precisely 
similar way to that which he employed for depositing sodium. 
Since that time it has been found, that even a feeble electric 
current from two or three cells of any ordinary battery, 
passed through a solution of the common salts of potassium 
(not, however, including the nitrate, or chlorate ?, bromate ?, 
or iodate ?) into a cathode of mercury, converts that 
metal more or less into an amalgam of potassium ; and if 
the cathode is composed of a metal which does not readily 
absorb the deposit, the latter at once decomposes the water, 
setting free hydrogen, and forming potash. For instance, 
according to Faire and Roche, in the electrolysis of solu- 
tions of alkaline carbonates or bicarbonates, the molecule 
splits up in such a way, that an atom of potassium or sodium 
is set free at the cathode and liberates hydrogen (' Chemi- 
cal News,' vol. xxx. p. 63; 'Journal of the Chemical Society,' 
vol. xii. p. 861). Buff also electrolysed potassic sulphides, 
and concluded that the metal travelled towards the cathode, 
and the sulphur towards the anode (' Chemical News/ 
vol. xv. p. 279). 

Faraday found, that by passing an electric current through 
melted iodide of potassium, iodine was set free at the anode, 
and potassium at the cathode. Jaquin observed, that fused 
sulphide of potassium yields, by electrolysis, potassium at 
the cathode. Mathiessen states, that a fused mixture of the 



3 00 The Art of Electro-Metallurgy. 

chlorides of calcium, potassium, and sodium, yields a deposit 
of potassium, when electrolysed in a certain manner (Watts, 
' Dictionary of Chemistry,' vol. i. p. 715), According to 
Brester, in the electrolysis of melted caustic potash, an anode 
of either platinum, silver, or copper, dissolves in the fused 
alkali, and the respective metals are deposited upon the 
cathode. The electrolysis of melted chlorate of potassium, 
with a platinum anode, yields potassium, which unites with 
a cathode of copper or platinum. Chlorine and oxygen 
(having an odour of phosphorus), are set free at the anode, 
and form thick white vapours by contact with water (' Chem- 
ical News,' vol. xviii. p. 145). 

The following experiments of mine, now first published, 
bear upon the simultaneous liberation of potassium and fluo- 
rine, by means of electro-deposition: — I fused 130 grains of 
pure fluoride of potassium in a platinum crucible, within a 
partially covered clay muffle (see fig. 29, p. 296) inserted in the 
hole in the top of one of my gas furnaces, and electrolysed it 
during two and a half hours, by means of a current from six 
Smee's cells, and two flat helices of platinum wire as elec- 
trodes. There was free conduction, and much gas (of an 
odour like that of hydrofluoric acid), evolved from the anode, 
but none from the cathode, and no signs of any deposit. 
The anode was not corroded, nor altered in weight. I also 
electrolysed some of the same salt in a state of fusion, by 
means of a current from six Grove's cells, with a thick 
platinum wire as the anode, and the platinum vessel as the 
cathode; great heat was evolved, and violent electrolytic action 
occurred; nearly white-hot metallic globules also accumulated, 
and exploded repeatedly. The end of the anode fused, and 
particles of platinum ramified from it in white-hot threads, 
and a short electric arc (about one-tenth of an inch in 
length) was produced. 

I also perfected and used, a somewhat elaborate platinum 
apparatus, by means of which the gas from the anode, was 
prevented from coming in contact with the cathode, and 



Electrolysis of Potassic-Fluoride. 3c 1 

might be collected ; the electrodes being enclosed within 
(but isolated from) two wide platinum tubes. One thousand 
grains of the perfectly pure salt was electrolysed in this 
apparatus, by means of a current from six Grove's cells. The 
anode, which was a solid rod of platinum, was rapidly cor- 
roded, and was thus cut off at the level of the liquid, and 
stopped the current ; the corroded surface was very bright, 
as if fused. Potassium was deposited upon the cathode. 
Much spongy platinum was diffused in the melted salt; 
and the apparatus was a little corroded at the surface 
of the liquid. No gas was evolved at the anode. The 
deposited potassium did not alloy with the stout rod of 
platinum used as the cathode. 55*35 grains of grey metallic 
platinum were found in the saline mass. A salt of platinum 
appeared to have been formed at the anode, then dissolved 
or diffused throughout the liquid, and decomposed by the 
heat, and thus the liberated fluorine did not escape at the 
anode, but was evolved in the mass of the liquid generally, 
and came into contact with the liberated potassium. 

Having ascertained the electrical relations of palladium, 
gold, platinum, and iridium in the fused fluoride, palladium 
being the most positive, and iridium the most negative, I 
repeated the experiments with an anode of iridium, and a 
current from three Grove's cells. Copious clouds descended 
at once from the anode, and made the liquid opaque \ there 
was also a violent action at the anode, it became black, 
and a little gas was evolved from it, accompanied by an acid 
odour, like that of a mixture of sulphurous anhydride and hy- 
drofluoric acid. Potassium was freely liberated at the cathode, 
and produced occasional explosions. With a current from 
six cells, the anode dissolved rapidly, and soon lost thirty- 
eight grains. I then put a pure gold anode, and employed 
two cells. Gas, of a feebly acid odour, was freely evolved at 
the anode ; and with a current from six cells, was very copious, 
and smelt much like sulphurous anhydride. The gold dis- 
solved much less rapidly than the iridium. With a palladium 



302 The A rt of Electro-Metallurgy. 

anode, and a current from six cells, the anode rapidly dis- 
solved, potassium was deposited, and exploded frequently; 
and an odour like that of hydrofluoric acid, was strong, much 
gas being liberated. S3'3 grains of free metal was found in 
the saline mass. The platinum cathode was not corroded. 
The platinum anode was dissolved as if melted; the iridium 
one was black ; the palladium one was oxidised of various 
colours. The platinum vessel was cut into, at the level of 
the surface of the liquid, evidently not by the fused fluoride 
of potassium, but by some substance, set free at the anode 
by electrolysis. In another instance, I electrolysed the 
pure fused fluoride with a large platinum anode, small 
platinum cathode, and a current from three Grove's cells, 
during half an hour. Much gas, having an odour of ozone 
and hydrofluoric acid, was evolved from the anode ; and 
the latter dissolved rapidly, and lost thirty-seven and a 
half grains in weight. The gas reddened test-paper. The 
platinum containing vessel was corroded at the line of surface 
of the liquid, and lost about eleven grains. About fifty-one 
grains of free metallic platinum, in loose powder, was found 
in the saline residue. Each of these experiments shows 
that a very corrosive substance was liberated at the anode. 

I electrolysed the fused salt with a gas-carbon anode, and 
a platinum wire flat helix as cathode, with a current from six 
Smee's cells. Free conduction occurred, and much gas was 
set free from the anode only. The part of the anode in the 
liquid was not visibly corroded. 

I also electrolysed about eight ounces of pure double 
fluoride of hydrogen and potassium (kf, hf) in a fused state, 
during half an hour, at about 300 Fahr., with a current from 
ten Smee's cells, and electrodes of stout sheet platinum. 
There was copious conduction, and abundance of hydrogen 
evolved at the cathode, but no gas from the anode, which was 
rapidly corroded away, with a rough surface, and lost 9^37 
grains. The salt became less fusible by loss of hydrofluoric 
acid, which escaped freely all the time. The saline residue 



Electrolysis of Pot as sic- Fluoride. 303 

contained a small amount of dissolved platinum salt, and 
nearly nine grains of free metallic platinum. In a second 
experiment, lasting half an hour, the salt was kept only just 
fused, and a small gold anode was employed. The con- 
duction was free, and much gas was evolved from the cathode, 
and a film of bright yellow gold spread over the surface of the 
salt, and connected the electrodes, unless the liquid was 
continually stirred. The anode rapidly dissolved (more 
quickly than that of platinum), and the salt of gold at once 
decomposed, and set free finely divided gold as a dull red- 
brown powder at the anode. No gas appeared at the anode 
at any time ; that from the cathode, detonated on applying a 
light. There was loose red-brown powder of gold, weighing 
1 '4 grains, upon the cathode, but only a faint gilding, weigh- 
ing '05 grain. The anode was corroded, dull and rough, and 
it lost 6 -So grains. The saline residue contained no dissolved 
gold, but 5*85 grains of red-brown powder, containing 5-30 
grains of gold. In a third similar experiment, by using a large 
sheet platinum anode, and a small platinum cathode, and a 
current from ten Smee's cells, during two hours, the phe- 
nomena were the same as in previous experiments. The 
anode lost twenty-eight grains ; much loose platinum col- 
lected on the cathode, which was neither corroded, nor 
alloved. The saline residue contained a trace of dissolved 
platinum salt, and nearly all the corroded platinum in a 
metallic state. In a fourth experiment I continued the 
V.ction during three and a half hours ; the results were as 
before. The loss of the anode was 3573 grains. The 
saline residue contained a small quantity of dissolved 
double fluoride of platinum and potassium, which, after 
being well washed, was dried, and heated to redness ; it 
then shot about as if gas was evolved from it. In a fifth 
similar experiment, lasting four and a half hours, at the 
lowest possible fusion temperature, more of the brown pla- 
tinum salt formed at the anode, and dissolved in the liquid. 
The anode lost 64-81 grains. In a last experiment I electro- 



3 04 The A rt of Electro-Metallurgy. 

lysed a gently fused mixture of 900 grains of the pure double 
salt, and one hundred grains of pure argentic fluoride, with 
a large anode of platinum, and a large cathode of silver. 
Conduction was complete with ten Smee's cells. No gas 
was evolved at either electrode. The surface of the anode 
disintegrated rapidly, and lost 49*84 grains in four and a half 
hours' action. The separated platinum dissolved only to a 
small extent in the liquid, and subsided, in admixture with 
the silver, to the bottom of the vessel, as a fine black powder, 
weighing 73*93 grains, which lost less than two per cent, when 
heated to redness. Some grey silver powder was deposited 
upon the cathode. In all these experiments with the acid 
fluoride, films continually formed upon the surface of the 
liquid ; they came from the cathode, and were more abun- 
dant, the deeper the cathode was immersed. 

According to Faraday, an aqueous solution of nitrate of 
potassium conducts electricity very well, yielding hydrogen 
gas at the cathode (it also gives ammonia at the cathode 
[Daniell]). He also observed that an aqueous solution of 
cyanide of potassium, yielded by electrolysis, hydrogen and 
potash at the cathode ; at the anode no oxygen was evolved, 
but the adjacent liquid became brown; that solutions of 
sulphocyanide, and ferrocyanide of potassium behaved simi- 
larly; also that fused cyanide behaved like its aqueous solu- 
tion. (Gmelin's • Handbook of Chemistry,' vol. i. p. 458=) 

I electrolysed a nearly saturated aqueous solution of 
pure fluoride of potassium, by means of a current from six 
Grove's cells, with large platinum electrodes ; conduction was 
copious, and the liquid acquired a nearly boiling temperature. 
Much gas (having an odour like that of a mixture of ozone 
and chlorine) was evolved at the anode. A saturated solution 
of the same salt, electrolysed by a current from ten large 
Smee's cells, with large platinum electrodes, evolved gas at 
' each electrode ; that from the anode smelt powerfully of 
ozone, and re-inflamed a red-hot splint. Several other ex- 
periments, with variations in the sizes of the electrodes, 



Deposition of Rubidium and Ccesium. 305 

were made, and with addition of hydrofluoric acid ; but the 
results were similar. 

I saturated some pure dilute hydrofluoric acid of 40 per 
cent, at 6o° Fahr., with pure double fluoride of hydrogen 
and potassium, and electrolysed the solution by a current 
from ten Smee's cells, a gold anode, and a platinum cathode, 
during five and a half hours. Gas was evolved freely from 
both electrodes, and a strong odour of ozone was observed. 
The anode lost 173 grains; and the cathode acquired first 
a gilded appearance, and then a black coating, and the liquid 
became black with finely divided matter. 

Bourgoin electrolysed a concentrated solution of neutral 
tartrate of potassium ; gas was evolved from each electrode, 
and alkali set free at the cathode. The anode became coated 
with acid tartrate, and evolved nitrogen, oxygen, carbonic 
oxide, and carbonic anhydride. The effect of the current 
upon a solution of the neutral tartrate, mixed with free alkali, 
was very different ; oxygen, acetic acid, carbonic anhydride, 
carbonic oxide, hydride of ethylene, and acetylene, were set 
free at the anode (' Chemical News,' vol. xvii. p. ^t>)' 

42. Kubidium. — Electro-chem. eqt. = 85, and Caesium, 
electro-chem. eqt. = 133. These metals have also been 
electro-deposited into a cathode of mercury, in a similar 
manner to potassium, sodium, and other highly electro- 
positive elements. 

43. Ammonium. — H 4 N. Electro-chem. eqt. = 18. Nearly- 
all the salts of ammonium are freely soluble in water, and 
may be made, by adding aqueous ammonia, or a solution of 
the carbonate, to the respective acids, and evaporating the 
solutions. 

Electrolysis of anhydrous ammonia. — Anhydrous ammonia, 
liquefied by pressure, has been eleotrolysed by Bleekrode, 
with a current from eighty Bunsen's cells ; gas was evolved, 
and the liquid became of an intensely blue colour. He also 
operated with a current from 3,240 cells of the chloride of 
silver battery of Mr. W. De la Rue \ the anode became 

x 



306 The Art of Electro-Metallurgy. 

black, much gas was evolved, and the liquid became deep 
blue. On stopping the current, the liquid became colourless. 
By dissolving rubidium, potassium, sodium, or lithium in 
such a liquid, I also obtained deep blue solutions (' Proceed- 
ings of the Royal Society,' No. 141, 1S73 ; also vol. xxv. 
P- 3 2 3) ) probably, therefore, metallic ammonium was set 
free and dissolved. 

Electrolysis of salts of ammonium. — Sir H. Davy electro- 
lysed a saturated solution of salammoniac, with an anode of 
platinum and a cathode of mercury; chlorine was evolved 
at the former, and the mercury became alloyed with ammo- 
nium, and swelled to a very large bulk. 

Hisinger and Berzelius found, that on electrolysing a 
solution of salammoniac with silver electrodes, hydrogen 
was evolved at the cathode, and oxygen at the anode, and 
the latter electrode acquired a coating of argentic chloride. 
They also electrolysed a mixture of aqueous ammonia and 
sulphate of ammonium. Hydrogen was evolved at the 
cathode, and nitrogen, mixed with some oxygen, at the 
anode. A gold anode, dissolved in such a liquid, became 
covered with brown fulminate of gold, and the cathode was 
gilded (Gmelin's ' Handbook of Chemistry,' vol. i. p. 458). 

According to Seebeck, a moistened cup of carbonate of 
ammonium, filled with mercury as a cathode, yields by elec- 
trolysis, the ammoniacal amalgam. Faraday electrolysed 
fused nitrate of ammonium ; hydrogen gas, mixed with a 
little nitrogen, was deposited at the cathode. The aqueous 
solution of that salt, similarly treated, yielded the same 
mixture at the cathode, and oxygen at the anode. I electro- 
lysed gently fused ammonium fluoride, by means of a current 
from six Grove's cells, a thick platinum wire anode, and a 
large platinum sheet cathode. The conduction was copious, 
and heat was evolved. Much gas was liberated at the anode, 
but no odour of ozone. 

Dry nitrate of ammonium condenses gaseous ammonia, 
and becomes a liquid ; the solution is a good electrolyte, and 



Deposition of Metalloids. 307 

yields ammonia and hydrogen at the anode. Anodes of 
silver, copper, lead, zinc, and magnesium, dissolve in it, but 
one of mercury becomes coated with an insoluble compound. 
When the anode is corroded, no nitrogen is liberated from it 
(Divers, ' Chemical News,' vol. xxvii. p. 37; 'Proceedings 
of the Royal Society,' vol. xxi. p. 109). 

According to A. Favre, under the influence of the cur- 
rent, ammonic-oxide is decomposed thus: — 1st. 3(NH.,). 2 
O = 3(NH 4 ) 2 + 3 . The three equivalents of ammonium 
set at liberty, decompose the water like potassium or sodium, 
thus:— 2nd. 3(NH 4 ) 2 + 3H 2 = 3 (NH 4 ) 2 + 3 H 2 . The 
oxygen of equation No. 1, reacting upon the ammonium, 
gives: — 3rd. + NH 4 = N + 2H9O. The first equation 
represents the electrolysis proper (' Journal of the Chemical 
Society,' vol. ix. p. 985). 



CLASS VII. DEPOSITION OF METALLOIDS. 

TITANIUM — SILICON — BORON — CARBON — PHOSPHORUS — 
SELENIUM — SULPHUR — IODINE — BROMINE — CHLORINE — 
FLUORINE — OXYGEN — NITROGEN. 

Although this book is one on the electro-deposition of 
metals, it can hardly be considered complete, unless some- 
thing is said about the deposition of the metalloids or non- 
metallic elementary substances, because the two classes of 
bodies are so closely related to each other in the electrolysis 
of their compounds. 

44. Deposition of titanium. — Elec.-chem. eqt. = — 

4 
= 12-5. This element does not appear to have been yet 
electro-deposited. Titanic acid is the most usual com- 
pound of it obtainable in a state of purity ; it dissolved 
very slowly in pure dilute hydrofluoric acid, and by evapo- 
rating the solution to dryness, a white and somewhat deli- 
quescent salt remained. I found that a heap of crystals of 

X2 



308 The Art of Electr o- Metallurgy. 

nitro- cyanide of titanium, conducted freely, an electric current 
from sixty Smee's elements, and that a single crystal pressed 
between the terminal wires, became red-hot, and then ex- 
hibited a splendid white light. 

o 

45. Silicon. — Elec.-chem. eqt.= — =7-0. In some ex- 

4 
periments with silicon (which I had fused into lumps) I found 
that the pieces conducted sparingly, a current from twelve 
Smee's elements; and that in dilute sulphuric acid, the 
silicon was strongly, but only temporarily, electro-positive to 
platinum. Silicon is generally strongly electro-positive to 
other substances in fused fluorides, and like carbon, is much 
more electro-positive at very high temperatures ; at such 
temperatures, it sets free sodium from its fluoride (see p. 297), 
Some of the electrical relations of silicon have already been 
given (see pp. 66, 67). Phipson states that magnesium 
separates silicon from silica at a high temperature (' Proceed- 
ings of Royal Society,' vol. xiii. p. 217; 'Chemical News,' 
vol. ix. p. 219). 

According to Becquerel, crystals of silicon may be de- 
posited upon a platinum cathode, in a saturated solution of 
gelatinous silica in hydrochloric acid (' Chemical News,' vol. 
xii. p. 4). According to Golding Bird, silicon may also be 
deposited from a solution of its fluoride in alcohol (' Philo- 
sophical Transactions of the Royal Society,' 1837, p. 37 ; 
Golding Bird's ' Natural Philosophy,' 5th edition, p. 408). 
I electrolysed fused pure silico-fluoride of potassium in a 
platinum vessel, with platinum electrodes; silicon was de- 
posited upon the cathode, and formed a fusible alloy with it. 

46. Boron.— Elec.-chem. eqt. = — =10-33. Phipson 

states, that magnesium in contact with boracic acid in a fused 
state, liberates boron (' Proceedings of the Royal Society/ 
1864, vol. xiii. p. 217; ' Chemical News,' vol. ix. p. 219). 

'Boron was first electro-chemically isolated by Davy. 
He states that when boracic acid is exposed between two 



Dep 



eposition of Silicon, Boron, and Carbon. 309 

Surfaces of platinum, receiving at the same time all the action 
of a current from 300 cells, an olive-brown matter is formed 
upon the negative surface, gradually increasing in thickness, 
and finally becoming black. The isolated body is boron.' 
(' Chemical News/ vol. xii. p. 3.) Fused borax yields oxygen 
gas at the anode, and boron at the cathode. The boron is 
separated by indirect action ; the current resolves the soda 
into oxygen and sodium, and the latter separates boron 
from the boracic acid (Faraday, Gmelin's ' Handbook of 
-Chemistry,' vol. i. p. 460). According to Burckhard, pure 
boracic acid in a state of fusion is a non-conductor, but fused 
borax conducts,' suffers electrolysis, and a series of com- 
pounds are formed or volatilised ; but the chief result is. 
that the salt is resolved into oxygen at the anode, and soda 
and boron at the cathode (* Chemical News,' vol. xxj. 
p. 238). I have found that by the electrolysis of pure boro- 
fluoride of potassium in a fused state, with platinum elec- 
trodes, the cathode became rough and brittle, by being 
converted into a compound with electro-deposited boron. 

47. Oarbon. — Elec.-chem. eqt. = — =3*0. According 

4 
to Phipson, magnesium in contact with carbonate of sodium 
at a high temperature, sets free carbon abundantly ('Proceed- 
ings of the Royal Society,' 1864, vol. xiii. p. 217; 'Chemi- 
cal News,' vol. ix. p. 219). Deville states, that metallic 
aluminium deposits carbon, from carbonate of potassium in 
a state of fusion ('Chemist,' New Series, vol. iv. p. 481). 

I have electro-deposited perfectly pure carbon, from the 
pure carbonates of potassium and sodium in a state of fusion, 
adding in some cases a little silicate of potassium, or fluoride 
of silicon and potassium ; the deposit was black, non-crystal- 
line, insoluble in all acids, burned with a glow, and left no 
residue. According to P. Burckhard, fused carbonate of 
sodium is a good conductor, and yields by electrolysis, 
carbonic anhydride, soda, and a small portion of carbon 
(' Chemical News,' vol. xxi. p. 238). Researches on the 



3 1 The A rt of Electro-Metallurgy. 

electro-deposition of carbon are interesting, with reference 
to the possibility of the artificial formation of diamonds. 

I have found that carbonic anhydride, liquefied by pres- 
sure, does not conduct a current from forty Smee's elements,- 
and is a powerful insulator of electricity (' Transactions of 
the Royal Society,' i86r, p. 85). According to Bleekrode 
and W. De la Rue, neither liquefied cyanogen (C 2 N 2 ), liquid 
carbonic anhydride (C0 2 ), carbonic bisulphide (CS 2 ), nor 
benzine (C 6 H 6 ), were decomposed by a current from 5,640 
cells of a chloride of silver battery (' Proceedings of the 
Royal Society/ vol. xxv. pp. 324-326). 

48. Phosphorus.— Elec-ch em. eqt.= 11= 10*33. The 

electric current resolves a solution of ordinary phosphate of 
sodium, into soda at the cathode, and phosphoric acid at 
the anode. The electrolysis of concentrated phosphoric 
acid, produces a metallic phosphide upon a cathode of copper 
or platinum (H. Davy). Acid phosphate of sodium in a 
state of fusion, yields hydrogen at the cathode (Faraday, 
Gmelin's ' Handbook of Chemistry,' vol. i. p. 460). Accord- 
ing to Burckhard, fused pyrophosphate of sodium, yields by 
electrolysis, phosphorus, oxygen, and soda; and, with a 
platinum anode, phosphide of platinum is formed (' Chemical 
News,' vol. xxi. p. 238). 

49. Selenium. — Elec.-chem. eqt. = '12-5 = 3975. 

2 

During the electrolysis of an aqueous solution of selenateof 
nickel, containing selenate of sodium, and free selenic acid, 
I have repeatedly observed an abundant deposit of bright 
red selenium upon a platinum cathode ; the deposition of 
selenium ceased on neutralising the acid with ammonia. 

50. Sulphur. — Elec-chem. eqt. = Ar = 16. A yelloAV 

solution of sulphide of potassium, yields a quantity of sub 
phur at the anode, and hydrogen gas at the cathode ; fused 
sulphide of silver is also slightly decomposed by electro- 



Deposition of Iodine, Bromine, and Chlorine. 3 1 1 

lysis, into sulphur at the anode, and silver at the cathode 
(Faraday, ' Gmelin's Handbook of Chemistry,' vol. i. p. 456)- 
An aqueous solution of sulphurous anhydride, yields sulphur 
and hydrogen at the cathode (De la Rive). 

51. Iodine. — Elec.-chem. eqt. = 127. Liquefied an- 
hydrous hydriodic acid (HI), does not conduct the current 
from eighty Bunsen's cells (Bleekrode, 'Proceedings of the 
Royal Society,' vol. xxv. p. 323). An aqueous solution of 
iodic acid, yields by electrolysis, oxygen at the anode, and 
iodine alone at the cathode. Concentrated hydriodic acid, 
yields iodine alone at the anode ; but the dilute acid gives 
iodine and oxygen. According to Faraday, fused iodide of 
potassium, or iodide of lead, yields iodine at the anode. 

52. Bromine. — Elec.-chem. eqt. = So. Anhydrous hydro- 
bromic acid (HBr), in the liquid state, does not conduct the 
current from eighty Bunsen's cells (Bleekrode, ' Proceedings 
of the Royal Society/ vol. xxv. p. 323). Aqueous hydro- 
bromic acid, deposits by electrolysis, bromine at the anode, 
and hydrogen at the cathode. 

53. Chlorine. — Elec.-chem. eqt. = 35*5. Liquefied an- 
hydrous hydrochloric acid (HC1), does not conduct the 
current, even from as many as 5,640 cells of a chloride of 
silver battery (Bleekrode and W. De la Rue, ' Proceedings 
of the Royal Society,' vol. xxv. p. 325). Concentrated hydro- 
chloric acid gives hydrogen at the cathode, and chlorine 
alone at the anode ; and only after considerable dilution 
with water, does oxygen begin to be deposited along with 
the chlorine. An aqueous solution of salammoniac yields 
chlorine at the anode, and hydrogen and ammonia at the 
cathode; and one of common salt, gives chlorine at the 
anode, and hydrogen and soda at the cathode. According 
to Faraday, fused chloride of lead, and chloride of silver, 
yield chlorine at the anode, and the metal at the cathode. 

54. Fluorine. — Elec.-chem. eqt. = 19-0. I have repeat- 
edly observed, that aqueous solutions of metallic fluorides, 
yield oxygen at the anode, because water is decomposed 



312 The A rt of Electro-Metallurgy. 

more readily than fluorides ; but with certain fluorides in a 
state of fusion, a highly corrosive substance is evidently 
liberated. (See the electrolysis of various fused fluorides, 
already described, especially that of fluoride of potassium, 
pp. 121, 300-303.) By the electrolysis of pure anhydrous hy- 
drofluoric acid (see p. 96), I found that the acid conducted 
readily a current from ten Smee's cells, but evolved no 
fluorine from an anode either of palladium (see p. 115), 
platinum (see p. 12c), or gold (see p. 126), and anodes of 
the densest varieties of carbon were instantly disintegrated. 
And by electrolysis of the pure aqueous acid, with elec- 
trodes of platinum, ozone and ordinary oxygen were alone 
evolved at the anode ('Phil. Trans. Roy. Society/ 1869, 
P- *73)- 

55. Oxygen.— Elec-chem. eqt. = L_ =8. Water, to which 

2 

almost any acid or salt has been added (in not too great 
quantity), in order to make it conduct, yields by electrolysis, 
oxygen at an anode of platinum. 

56. Nitrogen.— Elec-chem. eqt. == 14 4*66. A con- 

2 

centrated aqueous solution of ammonia, with electrodes of 
iron, yields hydrogen at the cathode, and pure nitrogen at 
the anode (Hisinger and Berzelius). 



313 



SPECIAL TECHNICAL SECTION. 



SECTION B. 

Having described all the methods in practical use for 
depositing metals, and as briefly as I have been able, the 
circumstances under which almost every known metal has 
been deposited, so that any one wishing to apply to practical 
uses, the deposition of metals not yet so employed, may be 
able to make a successful commencement, I will now give 
a number of special technical points of information, necessary 
for the successful prosecution of the art, which could not 
be so conveniently described in the preceding sections of 
the book. 

Fig. 30. 




General workshop arrangements. — Before commencing, 
on a practical scale, the art of electro-metallurgy, it will be 



314 The A rt of Electro-Metallu rgy. 

necessary to provide a depositing-room, vats for solutions, 
scouring and cleaning apparatus, batteries, a magneto-electric 
machine, or other source of electric power ; the various 
chemicals necessary for making and reviving depositing 
liquids acids for cleaning and ' stripping ' ; materials for 
making moulds, and preparing their surfaces, &c, &c. 

The establishment should consist of several rooms, and 
an open yard ; i.e., a room for depositing copper, another 
for silver, and a smaller and more private one leading out of 
it, for gilding. The rooms should be upon the ground-floor, 
on account of the weight of the vats containing the solutions, 
and should be provided with a cemented floor, and a drain 
running into a small cemented well, to recover valuable 
liquids which may be accidentally spilled. They should 
be well lighted and ventilated, because of the noxious vapours 
sometimes evolved ; and should contain conveniences for 
the placing of the vats, washing- troughs, and scratch-brush 
lathes ; and be provided with a plentiful supply of water. 
An outhouse for containing a large iron-boiler ; also a 
covered shed in a yard (for the processes of dipping), will 
be necessary. The yard is required for precipitating solu- 
tions, from which the poisonous vapour of prussic acid is 
evolved. Instead of an outhouse, a separate, but adjoining 
room, may be used, in which to erect the iron boiler, for con- 
taining caustic potash solution, for cleaning greasy and other 
articles. If voltaic batteries are much employed, they are 
best placed outside the plating-room, because the vapour 
arising from them is unhealthy, and also tarnishes the 
articles. If a magneto- electric machine is used, it is also 
best to have it, and the engine which drives it, at a distance 
from the cleaning liquids, or in an adjoining dry apartment. 

Accessible from each of the rooms, should be erected a 
low furnace, having a long horizontal flue covered with 
plates of iron, upon which are placed several large iron trays 
filled with hot sawdust, in which the wet articles are to be 
dried. Each depositing-room should be supplied with a 



Vats for Solutions. 315 

water-tap, and several large wooden tubs or troughs filled 
with water, for washing the articles. The ' pickling ' and 
' stripping ' liquids are best kept in large stoneware pans, 
under the open roof in the yard. In the gilding-room, will 
be placed iron vessels for containing the gilding liquids; these 
vessels are usually of enamelled iron, either wrought or cast, 
and should be supported on iron frames, with large Bunsen 
burners beneath, for the purpose of heating the liquids \ flues 
should also be provided to convey the products of combus- 
tion trom the burners into the open air. Accessible also to 
each of the rooms, should be placed several scratch -brush 
lathes, for scouring and brightening the articles. Round the 
walls of the coppering and silvering rooms, should be fixed 
well-insulated stout copper wires, to convey the electric 
currents from the batteries or magnetic machines to the vats. 
For the gilding-room these will not be required, because 
gilding is usually effected, by means of a small voltaic battery, 
or thermo-electric pile, placed close at hand. 

Vats for solutions. — The construction of the vats for 
containing silver solutions, has been already described (see 
p. 169) ; those for containing sulphate of copper solution, are 
usually made of wood, lined with a thick sheet of gutta- 
percha, so that the liquid shall not come into contact with 
the wood. According to Berthoud, a good mixture for lining 
vats to contain sulphate of copper solution, is composed of 
six parts of Burgundy- pitch, and one of gutta-percha, cut 
into very small pieces ; the whole being thoroughly mixed 
by melting and kneading. The silver-plating vats are some- 
times placed in the middle of the room, but more frequently 
against a wall where the sunlight does not fall directly upon 
the solutions. 

Cleaning articles for receivinga deposit. — All articles which 
are to receive a deposit, require to be made scrupulously 
clean, especially if it is wished to make the coating adhere 
firmly to the receiving surface. It is the practice before 
plating an article, to make its sur ace not only perfectly 



3 1 6 The A rt of Electro-Metallurgy. 

clean, but also smooth, by means of the revolving ' scratch- 
brush,' and by other methods. Articles of copper are 
usually, not * scratch-brushed,' but dipped. 

The processes of cleansing, are both of a mechanical and 
chemical nature. The mechanical means, are the usual ones 
of filing, scrubbing, and scouring, with various gritty materials. 
Emery-cloth is employed when the articles are dry, and fine 
silver- sand and a hand-brush, or piece of canvas, when they 
are wet. In addition to this, an instrument called a ' scratch- 
brush ' is continually used, and cannot be dispensed with. 

A ' scratch-brush ' is merely a bundle of fine and hard 
brass wires, about six or eight inches long, bound round very 
tightly with other wire, except at the ends (see fig. 31). 



Fir, 




These wires are of various degrees of fineness, and are 
also annealed to different degrees, to suit the various kinds of 
work. Four of such brushes are usually fixed in grooves 
upon the outside of the chuck of a lathe, so that the wires 
are parallel with the axis of the chuck (see fig. 32). Another 
form of scratch-brush, in which the wires are radial instead of 
parallel is shown in fig. 33. 

Fig. 32. 




To use these brushes, a lathe is required. A ' scratch- 
brush lathe,' suitable for cleaning small articles, is represented 
in the annexed figures $^ and 34. 

Above the revolving brush, is placed a cistern containing 
stale beer, a little of which is allowed to dribble upon the 



Cleaning Articles to receive a Deposit, 317 

articles during the process of brushing, and the brushes are 
surrounded by a screen, to prevent splashing. 

The chemical methods of cleaning, consist in immersing 
the articles for a greater or less period of time, in various 
acids or alkalies, according to the nature of the metals. 
Alkalies are usually employed hot, and are generally used 
for removing greasy, tarry, or resinous matters \ and acids 

Fig. 33- 




are generally used cold, after the greasy matters have been 
removed. The alkalies are kept in iron vessels, and the 
acids in stoneware pans, &c. 

The alkali commonly employed is caustic potash, because 
it is the strongest. A solution of it is prepared, by adding 
freshly-made cream of lime, to a boiling solution, composed 
of about half a pound or a pound of pearlash, to each gallon 



313 



The A rt of Electro-Metallurgy. 



of water, contained in an iron boiler, until a small quantity of 
the clear liquid gives no effervescence, on adding to it a few 
drops of dilute hydrochloric acid. The precipitate formed 
in the mixture, is carbonate of lime, and may be thrown 
away. As this liquid rapidly absorbs carbonic acid from 
the air, it should be kept covered as much as possible ; and 
a small quantity of the cream of lime, should be added to 
it occasionally, to renew its full degree of causticity. The 

Fig. 34. 




articles to be cleaned, are immersed for a short time in the 
boiling hot liquid ; copper only requires to be immersed a 
few seconds. Copper articles, joined by solder containing 
tin, must not remain long in the liquid, or the tin will dissolve, 
and be deposited upon the adjoining parts of the copper, 
and blacken them. 

Several kinds of acid liquids are employed, viz., dilute 



Cleaning Articles to receive a Deposit. 319 

sulphuric, strong nitric, and various mixtures of them. Nitric 
acid for dipping, contains about 10 percent, of sulphuric 
acid, and has a sp. gr. of about 1*52. 

The special methods of cleaning, depend both upon the 
nature of the impurities upon the surface, and of the metal 
beneath. All greasy articles, of whatever metal they are 
composed, are always dipped into the potash solution, and 
then usually thoroughly swilled in water. Articles composed 
of lead, tin, Britannia metal, or pewter, are dipped in the 
caustic potash, and, with or without swilling, transferred at 
once to the depositing solution. Those of zinc are some- 
times treated similarly ; and at other times, are, after swill- 
ing, dipped in dilute sulphuric acid, washed again, and trans- 
ferred to the plating liquid. For cleaning iron articles, a 
cold mixture of about twenty measures of water, and one 
of sulphuric acid, is frequently used ; but a better liquid 
is composed of one gallon of water, and one pound of sul- 
phuric acid, with one or two ounces of zinc dissolved in 
it ; to this is added half a pound of nitric acid. This 
mixture leaves the iron quite bright, whereas dilute sul- 
phuric acid alone, leaves it black, or of a different appear- 
ance at the edges. For glassy patches upon cast iron, 
(which usually consist of silicate of iron), hydrofluoric acid is 
used ; it is kept in a bottle of gutta-percha closed by a 
bung of indiarubber ; it must not be allowed to come into 
contact with glass vessels, nor must the mouth of the bottle 
be left open. The fumes from it are extremely dangerous 
to inhale. Articles of iron which have been cleaned in 
acids, and the adhering acid washed away with water, may 
be protected from rusting, by continued immersion in 
lime-water, a solution of washing-soda, or in water contain- 
ing any caustic alkali, until required. 

Articles of pure silver, are best dipped in a heated state, 
in dilute boiling sulphuric acid, after having been immersed 
in the alkali and swilled ; or they may be dipped cold, in 
strong and pure nitric acid, and then in distilled water. New 



3 2 o The A rt of Electro-Metallu rgy. 

anodes of rolled silver are often greasy, and have a film of 
oxide of iron upon them ; they should be scoured with caustic 
alkali, or be heated to redness, before placing them in the 
plating solution 

For articles of copper, brass, or German silver, a series of 
liquids is used ; — first, strong nitric acid; second, ' dipping 
liquid ' (consisting of sixty-four parts of water, sixty-four of 
sulphuric acid, thirty-two of nitric acid, and one of hydro- 
chloric acid) ; and, third, 'spent' liquid, i.e., either nitric 
acid or dipping liquid, which has become weak. Such 
articles are often partly cleaned, by heating them to dull 
redness, and then plunging them into dilute sulphuric acid. 
(Those having solder upon them are not heated thus ; 
articles of cast bronze are also not heated in this way, be- 
cause they would be liable to crack.) They are then soaked 
in old aqua-fortis, until, after rinsing, they look uniformly 
metallic ; they may then be dipped in strong aqua-fortis for 
a few seconds, and swilled. The straw-coloured aqua-fortis 
acts the best ; the white acts too feebly, and the red too 
strongly. It is necessary to have a large bulk of the acid, in 
order that it may not become too warm by the action. 

To dip gilding metal bright. — Immerse it in weak aqua- 
fortis until there is a black scale formed; then dip it in ' strong 
pickle' for a few minutes. (N.B. 'strong pickle' is exhausted 
aqua-fortis ; ' weak pickle ' is the same diluted with the wash- 
ings.) Then dip it quickly into strong aqua-fortis, and then 
into several waters in succession. There are various mix- 
tures, which may be employed for imparting a bright lustre 
by dipping ; the following is one of them : one measure of 
nearly exhausted aqua-fortis, two of water, and six of hydro- 
chloric acid ; the articles of copper, brass, or German silver 
should be immersed in it a few minutes, or until, after wash- 
ing off the black mud which entirely covers them, they look 
bright ; they are then cleaned and dipped again. To obtain 
a dead lustre, the articles of copper or its alloys, are dipped 
into a cold mixture of one volume of oil of vitriol mixed 



Cleaning Articles to receive a Deposit. 



321 



with two volumes of yellow aqua-fortis, and a little common 
salt then added ; the articles must remain some time in the 
bath, and then be quickly dipped into the liquid for pro- 
ducing a bright lustre, and immediately rinsed. Articles 
composed of German silver, are more difficult to impart a 
proper appearance to, by the process of dipping, than those 
of copper or brass. 

Old aqua-fortis is revived to a certain extent, by addition 
of oil of vitriol and common salt; the sulphuric acid decom- 
poses the nitrate of copper in it, and also the common salt, 
and sets free nitric and hydrochloric acids ; and crystals of 
sulphate of copper form at the bottom of the liquid. All the 
nitric acid may be utilised in this manner. 



Fig. 35- 




Fig. 36. 




Small articles are either strung upon wires (see fig. 35) 
of the same or similar metal, or they are put into a stone- 
ware basket (see fig. 36), and then dipped. Hooks and 
strong rods of copper, brass, &c, of the annexed forms (sec- 
figs. 37, 38), are necessary for suspending articles upon, 
for the purpose of dipping them into the various liquids. 
It is best that these hooks should be of the same material 
as the articles, because they are then less liable to cause a 

Y 



322 



The Art of Electro-Metallurgy. 



stain. Very small articles are placed in a basket or perfo- 
rated bowl, of stoneware or gutta-percha (see fig. 39), or a 
tray of platinum wire gauze (see rig. 40), to be dipped. 
Cleaned ones of brass, are immersed in a solution of argol, 
to keep them from oxidising. There should also be a series 
of vessels, containing water, for effectually swilling the arti^ 
cles. The pans for containing pickling, dipping, stripping, 

Fig. 37. 




Fig. 3?. 



Fig. 3Q. 




and quicking liquids, should be of the very best quality of 
salt-glazed stoneware. 

Sometimes, in order to assist in cleaning the articles, 
they are suspended for a short time in a suitable acid or 
cyanide liquid, in contact with the positive pole of a battery ; 
this dissolves the surface, and loosens the impurities, unless 



1 re 
I 






' Stopping-off' to prevent Deposition. 323 

they are very foul. In every case, they should be well rinsed 
with water, to remove the adhering acid, &c, before dipping 
them into the ' quicking' solution, or immersing them in tin- 
depositing vat. All objects which are to have a definite 
amount of metal deposited upon them, are weighed, and their 
weight noted, after they have been cleaned. 

' Stopping-qff 1 to prevent deposition. — Many articles which 
are to receive deposits, require to have portions of their sur- 
face ' stopped-off,' to prevent the deposit spreading over 
those parts ; for instance, in taking a copy of one side of a 
bronze medallion, the opposite side must be coatedwith some 
kind of varnish, wax, or fat, to prevent deposition ; or in 
gilding the inside of a cream-jug which has been silvered on 
the outside, varnish must be applied all round the outer side 
of the edge, for the same reason. For gilding and other hot 
solutions, copal varnish is generally used ; but for cold liquids 
and common work, an ordinary varnish, such as engravers 
use for a similar purpose, will do very well. In the absence 
of other substances, a solution of sealing-wax dissolved in 
naphtha may be employed. (See also pp. 182, 226.) 

' Quicking ' the surfaces of articles. — ' Quicking ' means 
coating the surfaces with a film of mercury, for the 
purpose of causing the deposited silver, &c, to adhere firmly ; 
the mercury acts, by offering a perfectly clean surface to 
receive the deposit, and, by dissolving to a minute extent, 
both the surface of the article, and that of the deposit, 
enables thera to mutually interpenetrate, and alloy with each 
other. 

Solutions of nitrate or of cyanide of mercury, are used 
for preparing the surfaces of copper, brass, and German 
silver, for receiving adhesive deposits of silver. The nitrate 
solution is prepared, by adding one ounce of mercury to 
sufficient nitric acid, diluted with three times its bulk of dis- 
tilled water, to dissolve it ; no more mercury must be added 
than the liquid will take up ; when completely dissolved, add 
about one gallon of water (see also pp. 143, 166). To prepare 

v 2 



3 24 The A rt of Electro-Metallurgy. 

the cyanide solution, dissolve one ounce of mercury as just 
stated, dilute it with water, and add a solution of cyanide of 
potassium to it, exactly as long as a precipitate is produced ; 
filter it, add a small quantity of water to the precipitate in 
the filter, and, when thoroughly drained, take out the pre- 
cipitate, and add to it, with stirring, a strong solution of 
cyanide of potassium, until it is all dissolved, then add a 
little more cyanide solution, and finally dilute it with water, 
until the whole measures one gallon. Another solution is 
composed of one part of pernitrate of mercury, and two 
parts of nitric or sulphuric acid, dissolved in 1,000 parts of 
distilled water; or, take nitric acid of specific gravity 1*383, 
add to it half its weight of mercury, and heat the liquid 
nearly to ioo° C. until yellow fumes are no longer evolved ; 
the solution should not be crystallized : dissolve one part by 
weight of this liquid in 1 ,000 parts of water, with which two 
parts of sulphuric acid have been previously mixed. Or, 
dissolve two ounces of mercury in two ounces of cold nitric 
acid, and then add three gallons of water; this forms a good 
solution. 

Almost any salt of mercury ('red precipitate' for instance) 
may be dissolved in a solution of cyanide of potassium, to 
form a ' quicking liquid.' Such a liquid is frequently made, 
by adding the cyanide to the nitrate, and not troubling to 
wash the precipitate. The objection to a solution of nitrate 
of mercury alone is, that as the quicking liquid cannot be 
readily washed completely away from hollow articles, the 
traces remaining in crevices, cause the silver to strip from 
those parts. Oxide of mercury, dissolved in a solution of 
cyanide of potassium, is often used as a ' quicking solution, 7 
but it is not as good for copper articles, as pernitrate of 
mercury containing a little hydrochloric acid. The solution, 
when prepared, is kept in a large stoneware vessel, with a 
pan of ' dipping liquid,' and two others containing water, near 
it ; and each placed near the scratch-brush lathe and de- 
positing vats, in the silvering-room. , 1 



' Quicking' Articles. 325 

'Quicking solution' should only contain sufficient dis- 
solved mercury, to make a copper surface immersed in it a 
few seconds, become white ; if the copper becomes black, 
the silver deposited upon it will not adhere ; it also shows 
that the solution of mercury is either exhausted, or not in a 
proper condition. Too much ' quick ' causes the silver to 
' strip; ' and usually too little can hardly be put on, but the 
amount varies in different cases. 

Articles which are to receive a thick coating of gold or 
silver, require a stronger mercurial solution, than those which 
are to receive a thin deposit, and they should be perfectly 
white and bright like silver, on coming out of the mercurial 
bath ; if the ' quicking ' has succeeded, they will have an 
uniform appearance. The solution will last a long time : 
when it gets nearly exhausted, it is liable to turn the articles 
which are dipped into it, of a dark colour; it is then better 
to prepare a fresh liquid, than to revive the old one. 

All articles, while still wet from the cleaning and quicking 
processes, should be quickly immersed into the depositing 
vat. The practical minutiae of preparing the surfaces < t 
different metals, for receiving adhesive deposits, vary in 
almost every manufactory, and much information yet remains 
to be developed upon this point ; for want of this knowledge, 
the most skilful operators sometimes fail in producing perfect 
adhesion, especially upon zinc, cast iron, steel, and Britannia 
metal. 

Wireing articles. — The articles have wires of copper 
attached to them, to suspend them by when in the vat. The 
wires differ in size ; with small objects, such as spoons, 
knives, forks, snuffers, teapots, jugs, &c, size No. 20 or 22 of 
the Birmingham wire guage, and about eighteen or twenty 
inches long, are used; very large ones, such as fire-irons, 
fenders, hat-stands, and pieces of ornamental iron-work, are 
suspended by strong copper or brass hooks. In some a 
where a powerful and certain connection is required, the 
wires are soldered to the articles. 



3 26 The A rt of Electro- Metallurgy. 

Voltaic batteries. — There are but few kinds of voltaic 
batteries usually employed in electro-metallurgy, and those 
which are used, are not often employed for operations of 
the greatest magnitude; in such cases, magneto-electric 
machines are rapidly superseding voltaic batteries, because 
they furnish electricity at much less expense, and their action 
is more uniform. I shall, therefore, only briefly describe such 
as have been commonly employed. 

Those most used in electro -deposition are, the old Wol- 
laston battery of zinc and copper plates in dilute sulphuric 
acid, Smee's, Darnell's, Bunsen's, and Grove's. 

Wollastoris battery. — The one which has been most em- 
ployed for electro deposition upon the large scale, is repre- 
sented in fig. 41. In consists of a large stone- 

Fig. 41. to ^ & 

ware jar, nearly filled with a mixture of about 

ten parts of water and one of oil of vitriol 
Across the top of the jar, is a moveable bar of 
well varnished wood, with a longitudinal and 
vertical groove in it, within which a thick plate 
of zinc may be raised and lowered, by means 
of a weight with a cord passing over a pulley : 
the great use of this is, to regulate the quantity 
of the current. To the edges or sides of the 
L|||l bar are fixed two sheets of copper, connected 
f£$k^ together by a copper band at their corners, and 
so attached, that they may be occasionally re- 
moved and cleansed; they extend nearly to the bottom of 
the liquid. Vertical rods of varnished wood, are fixed upon 
the under surface of the cross-bar, to prevent the zinc touch- 
ing the copper. The copper plates should not be allowed 
to remain many hours in the liquid, when the battery is not 
in action, because they then corrode, and form a small amount 
of cupric sulphate, which dissolves in the liquid, and this acts 
upon the zinc plates, and causes them to waste rapidly, because 
the zinc precipitates the copper upon itself, and thus a local 
battery is formed. If the copper plates remain long in the 




Voltaic Batteries. 



327 



Fig. 42. 



air in a wet acid state, they become covered with a badly 
conducting blackish film of oxide, and should be scrubbed 
with sand and a hard brush, and washed before being again 
used. 

Smeis battery. — This one has been extensively used for 
small operations, and is very convenient. It consists of 
amalgamated zinc and platinized silver, immersed in dilute 
sulphuric acid ; and is usually of the form shown by fig. 42. 
Two plates of zinc z z are held together (with a bar of var- 
nished wood between them), by means of 
a clamp binding-screw (see fig. 50, p. 335), 
and the sheet of platinized silver s, is 
fixed in a groove in the under side of the 
wooden bar, and attached to a pillar bind- 
ing-screw (see fig. 46, p. 335). The silver 
and zinc are prevented from mutual con- 
tact, by means of pieces of cork placed 
between them at their lower ends. It is 
important in this battery (and to a less 
extent in that of Wollaston) that the sul- 
phuric acid employed should be free from 
nitric acid; also that the negative plate 
should not come into contact with mercury. Platinized 
silver (i.e. silver coated with black platinum in a state of 
very fine division) is much more effective than silver alone, 
because with the latter metal, the bubbles of hydrogen 
evolved, adhere to its surface, and diminish the action, 
whilst with platinized silver they escape to the surface of the 
liquid rapidly. Platinized silver is also more electro-negative 
than silver alone, and still more so than copper, and therefore 
produces a stronger current. The mode of platinizing has 
already been described (see p. 118). 

DanielVs battery. — This one has also been largely used 
in electro-deposition, but its use for that purpose has dimi- 
nished. It consists essentially of amalgamated zinc in dilute 
sulphuric acid, and copper in a nearly saturated solution of 




328 



The A rt of Electro-Metallurgy. 



Fig. 43- 




cupric sulphate, the two liquids being prevented from mixing 
(but allowed to touch each other) by means of a porous par- 
tition. One of its forms is that shown in fig. 43, in which 
c, is a copper vessel forming the 
negative metal, and containing the 
cupric solution, and z, a bar of cast 
zinc, supported in the acid and water 
within the porous cell, by the wooden 
lid of that vessel. The copper cell 
has a large lip l, which is kept full 
of crystals of blue vitriol, to supply 
the loss of copper deposited upon 
the vessel ; it may also be used for 
the purpose of pouring out the solu- 
tion. 

The great advantage of this battery, is the uniformity of 
its action, and it is therefore called the ' constant ' battery. 
Fig. 44. It is sometimes constructed with the acid and 
water outside, and the copper plate and solution 
inside ; in that case a cylinder of rolled plate 
zinc is employed; it is also occasionally made of 
a rectangular form, with the porous cell of a flat 
shape. 

BuhserCs battery. — This kind is often em- 
ployed for gilding, two or three large cells being 
commonly used. It consists of amalgamated 
plate zinc in dilute sulphuric acid, and gas-carbon 
or Bunsen's coke, in strong nitric acid; the latter 
liquid being in a porous cell. The gas-carbon 
is usually in the form of thick rectangular bars, 
and in such cases the nitric acid is in a cylin- 
drical porous cell; but sometimes it is in the form 
of plates, and flat porous cells are then necessary. As 
the carbon is a porous substance, the acid rises in it by 
capillary action, and corrodes the metallic connections; the 
most effectual way of obviating this, is by using very long 



Relative Strength of Batteries. 



pieces of the substance, a considerable portion of each piece 
being out of the liquid, and putting a coating of varnish 
or paraffin upon them a little way down. Sometimes, in 
order to form a more secure connection, the upper end of 
the bar is coated with copper by electro-deposition ; or else 
it' is encased with metal by dipping it into melted 
lead. Fig. 44 shews a bar of carbon with its bind- 
ing screw attached. 

Grove's battery is precisely similar to Bunsen's 
in its essential parts, except, that it has platinum 
instead of carbon. The nitric acid and sheet of 
platinum, are contained in narrow flat porous cells 
of the form shewn in fig. 45. It is one of the 
strongest of batteries, but emits noxious acid 
fumes after having been some time in action, and 
its power soon declines. 

Relative strength of batteries. — The electro-motive force, or 
power of overcoming resistance (see p. 70), varies in different 
batteries, and is, according to Latimer Clarke, as follows : — 




Smee's (when in action) about 25 
Wollaston's(copperand zinc 
in dilute acid) . . 46 



Grove's .... 100 
Bunsen's . . . .98 
Daniell's . . . .56 
Smee's (when not in action) 57 

(See ' Electrical Measurement,' p. 108, by L. Clarke). 

From this table it will be observed, that the strength of a 
Smee's cell decreases during its working; this occurs very 
quickly after the current commences, because the internal 
resistance is increased by hydrogen gas adhering to the 
negative plate; after that has occurred, the current remains 
tolerably constant; a similar phenomenon happens with the 
Wollaston's element, but not with the Daniell's, because in 
the latter, the negative surface is kept free from that gas. 

' Relative advantages of different batteries.— Wollaston's 
is the most suitable one in cases where the resistance is not 
great, and where a large quantity of electricity, and long-con- 



3 3 o The A rt of Electro-Metallurgy. 

tinued action (as in depositing copper and silver) are re- 
quired, because its electro-motive force is small ; its action 
(after once it has commenced) is tolerably uniform, and large 
plates, and considerable bulks of exciting liquid, may be con- 
veniently employed. Smee's is suitable for similar cases, but 
where only a small quantity of electricity is required, because 
large plates of platinized silver are expensive. Daniell's is 
the best in cases where the resistance is greater, and a very 
uniform current is necessary. Grove's and Bunsen's are the 
most suitable where the resistance is still greater, and an occa- 
sional current of considerable electro-motive force, but not 
of long continuance, is necessary, as in gilding, and pre- 
paring for gilding {i.e. brassing or coppering) small articles of 
iron, steel, &c. in cyanide solutions. 

Exciting liquids for batteries. — In all these batteries, the 
zinc element is immersed in dilute sulphuric acid. The 
strength employed of this mixture, varies from one measure 
of acid and fifty of water, to one of acid and five of water; 
the usual strength with batteries such as Grove's and 
Bunsen's (which are soon exhausted), is one to five, but with 
Daniell's, Smee's, or Wollaston's, one to ten or twenty is a very 
good proportion. The price of concentrated sulphuric acid 
(oil of vitriol) is about three -halfpence per pound. It is impor- 
tant that this liquid be free from nitric acid (which it some- 
times contains), because that acid wastes the zinc, and in 
Smee's battery also corrodes the silver. To test for nitric 
acid, add to the suspected liquid, a small quantity of a solu- 
tion of indigo in pure sulphuric acid, and boil the mixture ; 
if the colour of the indigo does not disappear, nitric acid is 
not present. If the silver plates in a Smee's battery, become 
covered with a dirty whitish film, a trace of nitric acid is 
probably present. The nitric acid used in Grove's battery, 
should be free from hydrochloric ; otherwise, when it gets 
warm by the action of the battery, it will corrode and 
dissolve a little of the platinum plates. To ascertain if 
hydrochloric acid is present, dilute some of it with dis- 



L iqidds for Batteries. 



33 



tilled water, and add two drops of a solution of nitrate of 
silver : if a white cloud, or milkiness appears, that acid is 
present. Common oil of vitriol nearly always contains 
sulphate of lead dissolved in it, and when one measure 
of the acid is added to rive or ten measures of water, the 
mixture becomes cloudy, and a greyish white powder (con- 
sisting of the sulphate) settles to the bottom of the vessel ; 
this powder should not be allowed to get into the battery 
cells, otherwise it will settle upon the zinc plates, and cause 
them to waste. In mixing oil of vitriol and water, it is highly 
important that the acid should be gradually added to the 
water and not the reverse, and also that the mixture be stirred 
during the addition; and it is especially necessary, that the 
water and acid be cold, because great heat is evolved by 
mixing them ; if water be added to oil of vitriol, an explosion 
may be produced by the heat; and more especially is it 
dangerous to add hot water to oil of vitriol. Brown oil of 
vitriol is that which has been made from iron-pyrites obtained 
from the coal measures, and its colour is due to particles of 
carbon ; it is sometimes also impure ; but even the purest 
sulphuric acid is occasionally brown, from particles of organic 
dust getting into it. Strong sulphuric acid has a specific 
gravity of 1*845 ; if its gravity is less than this, it contains 
water. If the acid used in a battery is not sufficiently dilu- 
ted, crystals of sulphate of zinc are apt to form upon the 
bottom ends of the zinc plates after a time, through want 
of water to dissolve them, and this impedes the current ; 
a mixture of ten parts by measure of water to one of acid, is 
sufficiently dilute to prevent this; such a mixture has a specific 
gravity of about no. 

The only other liquid used in the batteries I have de- 
scribed, is a solution of sulphate of copper ; this salt is 
usually sufficiently pure, if a proper price (about sixpence 
per pound) is paid for it. Any green colour in it, is in- 
dicative of the presence of sulphate of iron, with which the 
cheaper varieties are contaminated. 



$2>2 The A rt of Electro-Metallurgy. 

Amalgamation of zinc. — Zinc rods and plates are always 
amalgamated, because it makes them more electro-positive 
(see p. 63), and because it also largely protects them from 
corrosion when the battery is not in action. The explanation 
of this is not very clear, but it probably is, that the mercury, 
by dissolving the surface of the zinc, and traces of foreign 
metals in it, renders the whole of that surface of uniform 
composition, and therefore no one part of it is relatively 
electro-positive or negative to another, and no local current 
can be generated. It is however dependent also upon the 
presence of a film of hydrogen upon the surface of the metal, 
for if a trace of nitric acid, or other liquid capable of oxi- 
dizing or removing such a film, is present, the mercury does 
not protect the zinc. 

Zinc rods or plates may be well amalgamated, by immers- 
ing them in dilute sulphuric acid until gas is freely evolved, 
then pouring mercury upon them, and rubbing them until 
they are bright all over. If the plates are new, they are 
probably greasy from the process of rolling, and should first 
be dipped in the caustic potash solution and swilled, before 
putting them into the acid, or they should be scraped. After 
having been amalgamated, they should be placed on their 
ends to drain off the superfluous mercury, and then the re- 
siduary mercury wiped off them. Ruhmkorff amalgamates 
zinc plates, by dipping them into a solution made as fol- 
lows : — Dissolve one part of mercury in five parts of aqua 
regia (i.e. one part of nitric and three of hydrochloric 
acids), and then add five parts of hydrochloric acid. An- 
other plan, is to put some mercury into a coarse flannel bag, 
dip the bag occasionally into dilute hydrochloric acid, and 
rub it upon the zinc plate or rod. 

Roseleur uses an amalgamating salt, prepared by boiling 
an aqueous solution of mercuric nitrate, with an excess of 
a powder, composed of equal parts of mercuric chloride and 
mercuric sulphate, cooling the mixture, and using the liquid 
only. The liquid is added to the mixture of sulphuric acid 



A malgamation of Zinc Plates. 



jjj 



and water, in those batteries only where two liquids are em- 
ployed. 

The mercury used for amalgamating should be pure ; 
if it contains tin, lead, bismuth, or copper, &c, these metals 
will adhere to the zinc, and cause great waste, by what is 
termed ' local action,' which means, that the zinc and the 
particles of foreign metal, being in contact in an acid liquid, 
constitute a multitude of little voltaic couples, which gene- 
rate electric currents (by corrosion of the zinc and waste 
of the acid), when the principal current is not circulating. 
For a similar reason, the zinc also should be free from 
metals less positive than itself. New zincs require frequent 
amalgamation, because the mercury soaks into them, but as 
they get old and thin by use, this mercury is left upon their 
surface, and therefore they rarely need to be amalgamated. 
When zinc plates become so thin as to fall to pieces on 
handling, new ones should be substituted, and the old ones 
may be melted, and cast into rods for Darnell's batteries ; 
or be broken up, put in an iron retort, and the mercury dis- 
tilled from them at a strong red heat, through a wide and 
wet tube of leather, into a vessel of water. 

Selection of zinc for batteries. — The best kind of zinc for 
batteries, and the kinds chiefly in use by electro- platers, are 
the Belgian and Silesian. The thickness of the plates should 
vary with the size of the battery ; the smallest should not be 
much less than one-eighth of an inch thick, on account of its 
brittleness when amalgamated ; large ones are generally about 
three-sixteenths or one-quarter of an inch in thickness. Zinc 
bolts for Daniell's batteries are sometimes made, by melt- 
ing together a number of old worn-out pieces of battery 
plates, and casting in a suitable mould. The wholesale price 
of unrolled (cake) zinc, is usually from twenty to thirty 
shillings per hundredweight. As all zinc contains traces of 
less positive metals ; when the former dissolves away, the 
latter come to the surface, and form an amalgam, and 
diminish the protective power of the mercury; such a coating 



334 The Art of Electro-Metallurgy. 

should occasionally either be scraped off, or removed by 
means of a very hard brush, and pure mercury applied. Cast 
zinc is not so good for electrical purposes as rolled zinc ; it 
is also less easy to amalgamate. Plate zinc may be cut by 
means of a saw with fine teeth, or by drawing a line across 
it repeatedly (using great pressure), with the end of a tri- 
angular file which has been ground to a sloping point. It 
may also be bent into cylinders whilst it is hot. 

Battery cells. — These are either of stoneware, glass, gutta- 
percha, or ebonite. For large cells, stoneware is nearly 
always employed : for small ones, glass is very good, and so 
is gutta-percha, but the preference is generally given to 
ebonite, especially for Grove's battery, because it is not 
brittle like glass, and does not become softened like gutta- 
percha by the heat generated in the battery. 

Porous cells for batteries. — These vary very greatly in 
quality : some are so slightly porous, that they very seriously 
hinder the passage of the electricity ; most excellent ones are 
manufactured by Messrs Wedgwood & Co. Formerly, porous 
cells of wood were employed, but now, only those of earth- 
enware are used ; they should always be kept in clean water 
when not in use, to remove nitric acid and salts of the bat- 
tery liquids from them, to prevent their cracking, and to 
preserve them always fit for immediate use. The degree 
of porosity of two cells may be compared by drying them, 
and then simultaneously filling them with water, and observing 
the appearance of their outer surfaces after one or two 
minutes. 

Binding-screws. — These are employed for connecting 
and holding together the plates, connecting wires, &c. of a 
battery. That shown by fig. 46 is for attaching to the wooden 
cross-bar and platinized silver plate of a Smee's cell ; 47 and 
48 are for attaching to zinc or copper plates ; 49 is for join- 
ing zinc and platinum, or zinc and copper plates together ; 
50 is for attaching to the top of a thick bar of carbon, or 
for holding together the zinc plates of a Smee's battery; 



Management of Batteries. 



COD 



and 51 is a screw I have devised and employed for joining 
together the ends of copper wires. 



Fig. 46. 



Fig. 47. 



Fig. 48. 






Fig. 49. 



Fig. 50. 



Fig. 






Management of batteries. — If the acid liquid in contact 
with the zinc is very strong, the zinc plates require frequent 
watching, to see that there is no local action, and when gas 
is seen or heard rising from them, or when any dull patches 
appear upon them, where the acid has acted too strongly, 
they should be amalgamated ; if this is neglected, great holes 
will be quickly corroded in them. They should be taken 
out of the cells every evening, if the acid liquor is at all 
strong, unless deposition is required to continue all night 

After a Wollaston's, Smee's, or Daniell's battery, has been 
at work a few days, a small amount of sulphuric acid should 
be added, and the liquid stirred, and this should be done as 
often as the current becomes feeble, until at length the liquid 
acquires an oily consistence, and becomes nearly saturated 
with zinc salt, which crystallizes upon the cells and plates 



3 3 ^ The A rt of Electro-Metallurgy, 

above the surface of the liquid ; it is then time to remove 
the liquid, and charge the battery afresh. If crystals of sul- 
phate of zinc are required for depositing or other purposes, 
the exhausted solution may be set aside, and allowed to 
evaporate. Sometimes in a Smee's or Wollaston's battery, a 
deposit of zinc forms upon some of the negative plates ; when 
this happens, it is a sign that the acid is exhausted in those 
cells ; either more acid, or a fresh mixture, should then be 
put in ; the deposit may also be removed, by immersing the 
negative plates in a separate portion of dilute sulphuric 
acid. 

Great care must be taken, that no mercury comes into 
contact with the plates of copper or platinized silver, the latter 
especially, as it makes them brittle, and greatly diminishes 
the electric power. To remove mercury from copper plates, 
the latter should be heated to redness, but with silver plates, 
a much less heat should be applied for a longer time, and 
then the plates should be re-platinized. Copper plates should 
be frequently scoured with sand with a hard brush ; and the 
silver plates should be re-platinized when they become light 
in colour, which will happen after about six months' careful 
working. 

In managing a Grove's or Bunsen's battery, it is highly 
important, not to allow any of the nitric acid to get into con- 
tact with the zinc, because it produces strong local action, and 
waste of that metal. As the nitric acid cannot be prevented 
from passing through the porous divisions, such batteries can- 
not be kept in continual energetic action more than a day, in 
consequence of this circumstance. The porous cells of such 
batteries should be soaked in water, the water being changed 
twice or three times (so as to extract all the nitric acid from 
them), before they are used a second time ; therefore, for con- 
tinual use of such a b?ttery, two or three sets of such cells 
are necessary, some being in soak whilst others are in use. 
In charging any two-liquid batteries, it is best to have the 
liquids level, and if they be either Grove's, Bunsen's, or 



Regulation of Electric Power, 337 

Daniell's, the liquid in the zinc division should be rather the 
higher. 

It is best to employ separate batteries for each different 
depositing liquid. Each battery should be tested before it is 
used : this maybe done in a rough, though usually sufncientlv 
accurate way for the purpose, if the current is a strong one, 
by connecting one end of the battery to a file, and drawing 
the point of the wire from the other end of the battery 
along its surface ; by the degree of brilliancy of the 
sparks produced, the strength of the current can be estima- 
ted. Before testing or using a battery, it is necessary to 
examine, and see that all the points of contact of the wires, 
screws, &c. are clean, and that the screws hold the wires 
firmly; it is also advisable to see that all th,e cells are con- 
nected in the right order, for if only one cell is connected 
the opposite way, it will not only be rendered ineffective, but 
will also neutralize the action of one of the others ; and its 
negative plate will be liable to dissolve by the influence of 
the current from the remaining cells. Voltaic batteries 
should be kept in a place of moderate and uniform tem- 
perature ; not where the liquids are liable to freeze, or rapidly 
evaporate. 

Regulation of electric power. — This is always a matter of 
considerable importance, especially when depositing from 
solutions, which will not bear a great range of electric force, 
without spoiling the quality of the deposited metal. It may 
be effected in a variety of ways, viz., by making alterations 
either in the battery, in the depositing vessel, or in the w 
connecting them. The electro-motive force (commonly called 
' the intensity ') of the current may be increased, by adding 
to the number of cells in the battery ; or by using cells of 
greater intrinsic pushing power, for instance Grove's instead of 
Smee's, &c. (see p. 327). As the electro-motive force is dimin- 
ished by resistance, a diminution of resistance in any part of 
the circuit will increase it ; this may be effected to a certain 
extent by making the depositing liquid hot, using larger 



3 3 8 The Art of Electro- Metallurgy. 

electrodes, or placing them nearer together. The quantity 
of the current may be increased by all these means, and also 
by immersing the battery plates, or only one of them, deeper 
in the liquid. The usual method, however, for regulating the 
electro-motive force of the current, is to alter the number of | 
cells in the battery ; and for regulating the quantity, to alter ; 
the depth of immersion of one of the battery plates (see j 
p. 326); but sometimes the latter cannot be conveniently 
effected, and in that case, the anode is either increased, or 1 
diminished in size. As that also is usually inconvenient, a , 
large piece of copper or brass is sometimes suspended to act as 
a cathode along with the article to be coated, and thus relieve 
it of part of the current. Galvanometers or voltameters 
(seep. 73) are very rarely employed to measure the electric 
currents employed in practical electro-deposition, chiefly, 
because the want of such instruments is not felt, and partly, 
because the processes are too coarse for the use of delicate 
apparatus. 

Compound voltaic batteries are usually so constructed, 
that they may be used to supply either a current of less 
quantity and greater electro-motive force, or the reverse.} 
By connecting a series, say of twelve cells, all in one row, \ 
with the metals alternating throughout, we obtain from the 
end wires, a current of a quantity of one, and an electro- 
motive force of twelve. By connecting them as a double!, 
row or series of six, the two end zincs being connected to 
one terminal wire, and the two end coppers to the other, wej 
get a current of a quantity of two, and electro-motive forcej 
of six. By connecting them in a similar way in a treble rowj 
as a series of four, we obtain a current, the quantity of which 
is equal to three, and the electro-motive force equal to four^ 
By arranging them in a quadruple row, and a series of threejj 
we get a quantity of four, and electro-motive force of three, 
By placing them as a sextuple row, and as a series of two- 
we get a quantity of six, and electro-motive force of twoi ... 
And finally by placing them in single row, connecting all the 1 



1 : 
:: 






Selection of Depositing Processes. 339 

zincs together by one wire, and all the silvers by another, 
they all act as one pair of twelve times the surface of a single 
cell, and we obtain a quantity of twelve, and electro-motive 
force of one. To make such arrangements successfully, it is, 
however necessary, that all the plates be provided with suit- 
able screws, also that all the cells be of a similar kind, and 
equal in electro-motive force, otherwise the currents from the 
stronger ones will be liable to pass partly through the weaker 
ones instead of through the plating solution, and also per- 
haps damage the battery, by causing some of the negative 
plates to be corroded ; it is therefore only occasionally that 
batteries are so arranged, i.e., not in single alternate series. 
The power of the current from magneto-electric machines, is 
usually regulated by interposing a piece of thin iron wire in 
the circuit. 

Selectio?i of depositing processes. — Different articles are 
electro- coated by different methods ; some are coated, as al- 
ready stated, by simple immersion, others by simple contact 
with zinc, and others by means of a separate current ; but 
an electro-plater usually employs only the latter method. 
For very small articles of which there are a great number, 
such as buttons, hooks and eyes, pins, &c, and which 
require only a very thin deposit, the simple immersion or 
wash process answers very well, being both easy of exe- 
cution, and cheap. But for all ordinary deposits, plating, 
&c, the separate current method is by far the best, because 
coatings of greater, and of sufficient thickness, of all ordi- 
nary metals, may be obtained by it, and the solutions do not 
usually (as in the other processes) require renewal. 

1 Pyro plating? — A process termed ' pyro-plating ' has 
during the last few years been introduced, and is stated to 
be specially suited for causing a coating of gold, silver, 
platinum, copper, nickel, brass, bronze, or aluminium- 
bronze, to adhere to metals, in cases where the metals to be 
plated, will not readily receive a film of mercury by the 

z 2 



340 The A rt of Electro-Metallurgy. 

ordinary ' quicking ' process, as with iron, steel, nickel, and 
aluminium. 

The article of iron, steel, &c, is first made perfectly 
clean, by immersion in a boiling solution of caustic alkali, 
then brushed with emery, also with a steel brush in a stream 
of solution of washing soda ; then suspended in a similar 
solution ; next made the cathode in a hot solution of caustic 
alkali, with a strong current to evolve from it plenty of hydro- 
gen, until its surface looks ' silvery ; ' and then transferred to 
a special solution of silver, and plated. A previously 
weighed metal plate, of equal amount of surface, is immersed 
as a cathode by its side, and weighed from hour to hour, 
until sufficient silver has been deposited. The original 
article is then removed from the vat, and (after washing?) 
heated in a furnace to * drive ' the coating of silver (or other 
metal as the case may be), into its surface ; and if the 
article requires tempering, it is quenched in water. Pyro- 
gilding is performed in a similar way to pyro-silvering, except 
that the whole of the metal is not put on at once, but in 
three successive layers, and heated in the furnace after 
each coating. The first, before being heated, looks per- 
fect, but by the heating, the gold nearly all disappears, 
being driven into the under metal. The second, only partly 
disappears by the influence of the heat ; and the third 
entirely remains. Pyro-gilding is specially recommended for 
coating articles of iron and steel ('Chemical News,' vol. xxvi. 
pp. 26 and 173). 

Selection of depositing liquids. — The most important 
points to be observed, in selecting a liquid for the separate 
current process, are : first, that it should yield its metal freely, 
and in a reguline state ; second, it should not decompose, or 
deposit its dissolved metal, by contact with the atmosphere, 
or by exposure to light ; third, it should not act chemically 
to any great extent, upon the base metals, or upon those to 
be coated ; fourth, it should dissolve the anode sufficiently 
freely ; fifth, it should possess good electrical conducting ' 

II 



Testing a Depositing Liquid. 341 

power ; sixth, it should not evolve gas at the surface of the 
articles. The three first conditions are, I consider, indispens- 
able, and if it fail in either, it is worthless or nearly so, for the 
purposes of electro-deposition. 

Testing a depositing liquid. — From what has just been said, 
the mode of testing is obvious. To test it, pass a current 
from two or three Smee's cells through it, by clean and 
weighed anodes and cathodes, the latter being composed of 
the particular metal which it is intended to coat. Observe 
the quality of the deposit, the speed of deposition, and 
whether much gas is evolved from the electrodes. Set a 
portion of the clear liquid aside, in a colourless glass vessel, 
exposed to light and air, and observe if it acquires a film, 
deposits a sediment, changes in colour, evolves gas, or 
shows any other signs of decomposition. Immerse in a 
separate portion, for about a quarter of an hour (that will 
be abundance of time), a bright and perfectly clean piece of 
metal, of the kind to be deposited, and observe if it becomes 
coated with the dissolved metal, or changes in appearance 
in any way. A liquid which requires a strong current to 
make it yield its metal freely, or which liberates gas at the 
cathode, but has no other defects, does no harm except being 
wasteful of the electric power. One which evolves gas 
at the anode, becomes gradually deprived of its dissolved 
metal. 

Praetieal management of depositing solutions (see also p. 
go et sea.). — Having obtained a good depositing liquid, we 
must manage to keep it so ; because a large vat of silver solu- 
tion, or a vessel of gilding liquid, is valuable. The operator 
should as far as possible, avoid doing anything to such 
liquids which will alter their chemical composition ; many 
valuable ones have been injured and spoiled, by persons 
(unused to making careful experiments) adding substances 
to them, with the hope of improving them. The tales told 
by electro-platers of their experiences with depositors, in 
making and mending electro-plating solutions, should act as 



3 42 The A rt of Electro-Metallurgy. 

warnings to those about to commence in the art upon a 
large scale. One discovered that the operator, by using 
cyanide of potassium, regardless of its strength, to make 
cyanide of silver, re-dissolved about sixty ounces of silver, 
and threw it away in the wash-waters. Another had a similar 
mishap with eleven ounces of gold. A third had 450 ounces 
of silver converted into waste residue. A fourth had two 
large vats of silver solution rendered incurable, by addition 
of too much 'brightening' liquid; and many electro-platers 
have had similar mishaps. Others have found their anodes 
dissolve with extraordinary rapidity, through the use of too 
much free cyanide, or by allowing them to remain in contact 
with the iron vat, and have been surprised to find, that a 
solution, which when made, contained only an ounce of 
silver per gallon, held in solution more than four times as 
much. Others, by keeping a record of the silver dissolved 
and deposited, as well as of that found in the liquid by an- 
alysis, have missed a considerable quantity, and ultimately 
found that it had soaked into the sides of the thick wooden 
vats. The composition of a depositing solution should not 
be altered, except so far as it can be done with perfect safety, 
as by diluting it to a certain extent with water, or adding 
materials to exactly re-place those abstracted from it The 
electric power should always be adapted to the liquid, and 
not the latter to the electric power. The electrodes should 
as a rule, be kept nearly equal in amount of surface, the 
anode being in some cases the largest ; and the quality of 
the deposit should not usually be regulated by altering their 
proportionate extent of surface, but by altering the battery 
or other source of the current. 

As a general rule, in order to prevent depositing liquids 
gradually becoming contaminated with foreign metals, any 
metal which will b'e corroded by a particular depositing 
liquid (and which will therefore coat itself by simple im- 
mersion in that liquid), should previously receive a coating 



Proper Position of Objects during Deposition. 343 

of suitable metal in a preparing solution • for instance, iron 
articles which are to receive a thick coating of copper, are 
first coated with a thin film of that metal in a cyanide 
liquid. 

Anodes of any metal may be formed of scraps, but that 
is not advisable, if better ones can be obtained. 

Proper position of articles a?id dissolving plates in the 
vats. — Both the articles and the plates should be wholly sub- 
merged in the liquid ; the former being a little the deepest. 
Both should be vertical, or nearly so ; the plates may however 
overhang a little with advantage : it makes them dissolve 
more evenly. The horizontal position, with the dissolving 
metal above, although the most scientifically correct ar- 
rangement, does not succeed in practical working, because 
the metal used for dissolving is never quite pure (with nickel 
and copper especially), and the impurities from it, fall upon 
the surface of the receiving article beneath, and make it 
rough ; in addition to this, the position of the article pre- 
vents its being easily removed or examined. If the object 
to be coated, has a very irregular outline, either the dis- 
solving plate should be bent somewhat to its form, so that 
the two may be nearly equidistant at all parts ; or the article 
should be often shifted in its position, so as to produce a 
nearly uniform thickness of coating all over. The nearer 
the receiving surface is to the dissolving plate, the more rapid 
is the deposition, and a large body of liquid, deposits more 
rapidly and more evenly than a small one. The greatest 
thickness of coating always takes place upon the most 
prominent places, i.e., upon those parts nearest the dis- 
solving metal. If it is desired to prevent vertical lines in 
a thick deposit, the object must be kept in motion; — the 
means of doing this has been already described (see pp. 
171-174). 

Motion of the articles is very advantageous : it permits 
much more rapid deposition \ it keeps the solution much 



3 44 The A rt of Electro-Metallurgy. 

more uniform in composition, prevents the lower portions 
of the objects being coated so much faster than their upper 
ones, and also prevents the upper parts of the anodes being 
dissolved so much more rapidly than their lower ones, In 
addition to this, by keeping the solution mixed, it greatly 
diminishes the electric conduction resistance, which would 
be produced by polarisation, due to layers of liquid of oppo- 
site electrical nature, collecting in contact with the electrodes 
(see p. 54). 

As most of the deposit takes place upon the parts of the 
article nearest the dissolving plate, if other parts require 
also a thick deposit, the article must be so placed, or an 
anode must be employed of such a shape, as to effect that 
object. 

Regulation of the deposit. — Regulation of the quality of 
the deposited metal is always an important matter, and with 
all metals, except a very limited number, it is one of the most 
difficult objects to effect. As a general rule, the greater the 
electro-motive force, and the smaller the quantity of the 
current, the harder and brighter is the deposited metal ; but 
this of course only holds good in the case of a liquid which 
is capable of yielding such metal. The chief points are, first 
to obtain a good liquid, at the proper temperature, and second 
to adjust the density of the current (see p. 38) until the re- 
quired kind of deposit is obtained. Some liquids are so 
constituted, (especially those of the more easily oxidizable 
base metals, such as manganese,) that if the current is only of 
sufficient density to deposit it in a bright reguline state, it is 
not sufficiently dense to prevent the metal at once taking up 
oxygen and forming a sub-oxide. If, in a good depositing 
solution of a non-readily oxidizable metal, such as copper, 
we are producing by means of a current of considerable 
electro-motive force, a black powder deposit, upon a very 
small article, a much larger article would receive by the same 
current a reguline deposit, and upon a very much larger 
one the deposit would be hard and crystalline. So much, 



Regulation of the Deposition. 345 

however, depends, in every case upon the special charac- 
teristics of the particular liquid, that these can only be con- 
sidered as general instructions for the guidance of the electro- 
depositor. This part of the subject has also been already 
treated of in previous parts of this book (see pp. 35-39, 54-55, 
and 90-93). 

The action of a current of great electro-motive power, 
but small in quantity, appears in some cases (for instance 
with copper), to confer upon the deposited particles, a kind of 
polarity, a power of grouping themselves into separate warty 
nodules or groups of crystals, each of which, as it becomes 
larger, appears to powerfully repel all particles in its neigh- 
bourhood, and thus causes the metal to spread rapidly ; when 
this action is continued to a considerable thickness of deposit, 
especially in cold weather, the metal is exceedingly hard, and 
easily broken into a number of distinct grains or nodules, which 
are in the form of lumps with rounded edges. With a current 
from 100 pairs of Smee's battery, acting for a long period of 
time in cold weather, and the quantity of the current kept 
down to the lowest possible degree, I have seen a tough 
deposit of zinc spread over several square inches of clean 
gutta-percha; and in depositing copper by a current of 
rather high intensity, and small quantity, upon black-leaded 
gutta-percha medallions, I have repeatedly observed, that 
where there was a sunken boundary line near the edge, the 
deposit remained quite thin, as if powerfully repelled, whilst 
on each side of the line it was very thick, and on the outside 
edge accumulated in large masses, hard and distinctly 
separate, and containing as much metal as the whole of the 
medallion besides. The effect of lines is often seen in 
electro-copies of set-up type, and the deposits are very fragile 
at those parts. 

With regard to the regulation of the quantity of the de- 
posited metal, that part of the subject has been treated of in 
the theoretical division (see pp. 39-44, 74-75). We know that 
when all the arrangements, are properly made and carried 



346 The Art of Electro- Metallurgy. 

out, the quantity of metal dissolved and deposited in the 
vat, is m direct proportion to the quantity of zinc dissolved, 
and acid consumed, in each alternation of the battery. With 
a perfect depositing liquid, good battery arrangements, and 
pure materials, for every equivalent of zinc, dissolved in each 
alternation of the battery, an equivalent of metal is dissolved 
on one side, and an equivalent deposited on the other, in 
the depositing vessel. For instance, for every equivalent 

[ -i= 32-5 parts ) of zinc so dissolved, and — =49 parts, 

or one equivalent, of oil of vitriol consumed in the battery, 

an equivalent 1 — — ' = 3175 parts J of copper is deposited 

in the sulphate of copper solution, or an equivalent (108 
parts) of silver in the cyanide of silver plating liquid, and a 
similar quantity of copper or silver dissolved at the anode. 
But in practical working, the materials are rarely if ever 
pure, or the arrangements perfect ; the zinc nearly always 
contains a small proportion of other substances, the mercury 
contains tin or lead, and the sulphuric acid contains a little 
nitric acid, or plumbic sulphate. The acid liquid of the 
battery is often too strong ; much of it is also thrown away 
before it is completely exhausted. The zinc plates are 
not kept well amalgamated, or the silver well platinized, or 
the plates are suffered to remain too long in the liquid when 
not in use. The metal of the anode is also frequently impure ; 
occasionally some of the deposit is allowed to re-dissolve, 
from the battery power becoming low, and from not stirring 
the solution ; in some solutions, a part of the electric current 
is expended in evolving gas at the cathode ; and finally, the 
repeated operation of ' scratching,' removes some of the \ 
deposit. Allowing for all these, and other unavoidable t 
sources of loss, in practical working, about one pound only \ 
of copper, can be deposited in the ordinary sulphate solu- 5 
tion, by the consumption of from one and a quarter to one 



Magneto- Electric Machines* 347 

and a half pounds of zinc, and an equivalent quantity of 
acid, in each alternation of the battery. 

With regard to regulation of the speed of deposition, (see 
p. 337) ; with every liquid there is a limit of rate of deposition 
per given amount of surface, beyond which it is impossible 
to obtain good metal (see p. 38), and that limit differs with 
every different liquid, and probably with each liquid at every 
different temperature, besides being dependent upon the 
kind of receiving surface. It is well known to electro-depo- 
sitors, that it is usually much more difficult to produce a 
reguline deposit upon rough surfaces, than upon smooth 
ones ; upon cast-iron than upon most other metals, and that 
to obtain it at all upon that metal, the rate of deposit 
must be less, than upon a smooth surface of pure copper 
or silver. 

Magneto-electric machines. — The fundamental principle of 
all magneto-electric machines, has been already stated and 
illustrated (see p. 57). As this is not a treatise upon 
dynamic electricity, but only upon the applications of it to 
metallurgical operations, and as the spa^e at my command 
is only limited, and a clear and full description of magneto- 
electric machines would occupy too much space, I am 
only enabled to insert a very brief statement respecting these 
electro-motors. 

Figures 52 and 53 represent Wilde's magneto-electric 
machine. It consists essentially of two electro-magnets, 
a small and a large one, with insulated copper wire coiled 
transversely upon them; and with armatures of soft iron 
(see fig. 53) (also with insulated copper wire coiled length- 
wise upon them), revolving between their poles. The residual 
magnetism of the small (or upper) electro-magnet, excites a 
feeble current in the coil of its revolving armature. This 
current circulates through the wires of both the magnets, 
and increases the magnetism ; and the increased magnetism 
of the small one, reacts upon the armature, and increases the 



34'3 The A rt of Electro-Metallurgy, 




Magneto-Electric Machines. 349 

current, and so on, until both the magnets are saturated with 
magnetism at the expense of mechanical power. The cur- 
rent from the revolving armature of the large one alone, is 
used for electro-deposition, or other purposes. ' The arma- 
tures of both machines are driven at a speed of about 2,000 
revolutions per minute, and at this rate, the current from 
the large one, deposits twenty-eight ounces of silver an hour, 
with an expenditure of two horse power.' 

These machines are in extensive use at the works of 
Messrs. Elkington and Co., in Birmingham, for the purposes 
of depositing copper statues, and for general plating with 
silver ; also at the copper works of the same company at 
Pembrey, near Swansea ; for purifying by electrolysis upon 
the large scale, crude slabs of unrefined copper from the 
ordinary smelting process. A single 'multiple armature ' ma- 
chine of Wilde's (see ' Philosophical Magazine,' June 1873), 
at those works, deposits four and a half hundredweights of 
copper in twenty-four hours. These machines have also 
been successfully applied to the economic production of 
coppered iron rollers for calico-printing. To keep the arma- 
ture cool, the ends of the large electro-magnet are made 
hollow, and a current of cold water caused to flow through 
the cavities. 

Gramme's magneto-electric machine is shown in fig. 54. 
It consists essentially of a ring of soft iron, covered with a 
large number of coils of insulated copper wire, the respec- 
tive ends of which are connected with the separate sections 
of two commutators fixed upon the axis of the machine. 
The ring with its coils and commutators, fixed upon the axis, 
revolves between the poles of an electro-magnet. 

By this machine — ' To deposit 600 grammes of silver 
requires one horse power, and a speed of 300 turns per 
minute ; the tension of the current being equal to that of two 
Bunsen's cells, and its quantity equal to thirty-two such cells 
of ordinary size. At a speed of 275 revolutions per minute, 
it has deposited 525 grammes of silver per hour; at 300 



350 



The Art of Electro-Metallurgy. 



turns, 605 grammes • and at 325 turns, 675 grammes. The 
weight of the copper wire on the fixed electro-magnets was 



Fig. 54. 




135, and on the moveable ones forty kilogrammes' ( c Tele- 
graphic Journal,' vol. i. p. 54). ' The present form of the 
machine as used for electro-deposition is composed as 
follows : — 



Total weight 

Copper coils . 

Total height . 

Total width . 

Deposits silver per hour 

Required power to work it 

(' Telegraphic Journal,' vol. iii. p. 



117*5 kilogrammes 

47'0 

•6 metre 

•55 „ 
600 • grammes 
5 o * kilogrammet res. ' 

). This machine is in 



Thermo- Electric Piles. 3 5 1 

use at Messrs. Christople's large electro-plating works in 
Paris. 

The most recent form of magneto- electric machine, is 
that of Messrs Siemens and Alteneck, a description of which, 
with engravings of it, may be found in the ' Electrical News,' 
vol. i. p. 226. 

The chief obstacle hitherto met with in the use of these 
machines has been, that after a few hours' action, the different 
parts are liable to become considerably heated, partly by the 
incessant molecular changes attending the variations of mag- 
netism, and partly by the conduction resistance in the coils 
of wire. This has been largely overcome in Mr. Wilde's 
machine by the employment of several small machines in- 
stead of one large one, and by allowing a stream of cold water 
to run through the hollow ends of the magnet. In Gramme's 
machine, provided it is not worked too fast, the heat is re- 
duced to a moderate amount; and in a large machine of 
Siemens and Alteneck's in the Vienna Exhibition, I also 
observed but little rise of temperature, after it had been in 
action a considerable time. Another objection to some of 
these machines, is the complexity of the commutator. The 
electric current from all these magnetic machines, is regulated 
for electro-metallurgical purposes, by interposing a piece of 
thin iron-wire in the circuit. 

Thermo-electric piles. — The two most efficient kinds of 
this instrument, appear to be those of Noe of Vienna, and 
Clamond of Paris. The former is the more quickly excited, 
and gives a powerful current; and the latter is the most 
strongly constructed. 

Noe's pile (see fig. 55) consists of small cylinders, about 
one and a quarter inches long, and three eighths of an inch 
diameter, of an alloy of about thirty-six and a half parts of 
zinc, and sixty-two and a half of antimony as the positive, 
and stout German-silver wire as the negative element. 
Twelve of these pairs have an electro-motive force of one 
Daniell's cell^ and twenty of them that of one Bunsen. The 



352 



The A rt of Electro-Metallurgy. 



resistance of twenty of them is about equal to one ohm (see 
PP- 7°— 73)- With a great external resistance, twenty of 
them are equal to one Bunsen's, and with a small external 
resistance, twenty quadrupled ones are somewhat stronger 
than one of Bunsen's elements (Watts' * Chemical Dictionary,' 
supplement, p. 458. Wiedemann's ' Galvanismus und Elek- 
tromagnetismus,' 1872, vol. i. p, 824. ' Journal of the Chemi- 
cal Society,' vol. ix. p. 989, vol. xi. p. 465). 

The construction of a few elements, is shown in the 
annexed figure. The junctions of the elements are heated 
by small gas-flames, and the alternate junctions are cooled 



Fig. 55- 




by the heat being conducted away by large blackened sheets 
of thin copper. To protect the German-silver wire from 
oxidation, it is enclosed in a tube of that alloy where the 
flame impinges against it ; and to prevent the ends of the 
positive cylinders being melted, they are faced with iron 
and a thin sheet of mica. The German-silver wire may be 
heated to low redness. The usual form of the apparatus is 
in ninety-six elements, which may be either used as ninety- 
six by one, forty-eight by two, or twenty-four by four; and 
instantly changed from one to the other of these arrangements, 



Thcnno-Ekctric Piles. 



353 



by means of a most ingenious and effective current ti 
poser, which does not require cleaning. The current 
attains its maximum strength in about one minute ; that 
from the single series decomposes water rapidly \ and that 
from the quadruple series excites a large electro-magnet 
powerfully. I have used this apparatus with great satisfac- 
tion for many brief experiments. The instrument is made 
by W. J. Hauck, Kettenbriickengasse 20, Vienna ; also by 
P. Dorfell, Berlin. It is, I am informed, in use for electro- 
plating in Dittmar's electrotype and lamp manufactory, 
Vienna. 

Fig. 56. 




Fig. 56 represents a small Clamond's pile, connected 
for intensity (see also 'Telegraphic Journal,' vol. i. p. 12). 



A A 



3 54 The A rt of Electro-Metallurgy. 

The elements are tinned sheet-iron as negative, and an alloy 
of two parts of zinc and one part of antimony as positive. 
A pile which consumes 150 litres of gas per hour, is capable 
of depositing one kilogramme of copper, at a cost of two 
francs fifty centimes (' Telegraphic Journal,' vol. iii. pp. 157 
and 319). According to the inventors, 'a machine of 100 
bars, with a consumption of 8 to 9 cubic feet of gas, deposits 
about an ounce of silver per hour. The same apparatus 
coupled for quantity, will deposit about one ounce of copper 
in the same time,' ' 100 bars, coupled for quantity, have 
an electro -motive force of about five volts, and an internal 
resistance of one ohm' (see pp. 70-75). Clamond's pile is I 
being used for electro-plating and depositing, in various \ 
establishments in Birmingham, London, Sheffield, and other 
places. Its durability is being improved. 

SPECIAL INFORMATION RESPECTING SUBSTANCES USED 
IN THE ART. 

As there are various substances used in the different pro- \ 
cesses of electro-deposition, it will be useful to the practical 
operator in the art, to be acquainted with some special 
technical points of information respecting them, which may 
affect the success of his operations, and which have not 
already been given in the body of the book. 

Water. — Distilled water is the most suitable for making 
solutions. It should give no cloud, on adding to separate fi 
portions of it, a few drops of solutions of argentic nitrate, 
chloride of barium, or oxalate of ammonium ; nor become 
brown on addition of sulphuretted hydrogen water. If dis- 
tilled water cannot be conveniently obtained, filtered rain- 
water may usually be employed in its stead. 

Nitric acid. — Called also aqua fortis. The pure acid for |. 
dissolving silver, &c, should be colourless, have a specific 
gravity of not less than 1*52 ; and separate portions of it, 
diluted with pure distilled water, should give no cloud with \ 



Substances used in the A rt. 355 

a single drop of solution of nitrate of silver, or of chloridi 
barium. It should be kept in a stoppered bottle, in a dark, 
cool, and dry place. If a drop of this or any other acid falls 
upon one's clothes, diluted aqueous ammonia should at on< e 
be freely applied. 

All the pure strong acids should be kept in stoppered 
bottles, in a dry place. Carboys of common acids, and dipping 
liquids, should have stoneware stoppers, and be kept in an 
outhouse. 

Hydrofluoric acid. — Called also fluoric acid. This liquid is 
always very impure. It should be kept in a bottle of gutta- 
percha, provided with a stopper of india-rubber, in a dry and 
cool place, and not in close proximity to glass vessels, 
because the vapour corrodes them. It is highly dangerous 
to breathe the fumes of this acid ; and if a drop of it falls 
upon the skin it should be thoroughly washed oft" at once, 
otherwise after a few hours great pain will be suffered. 

Hydrochloric acid. — Called also ' muriatic acid,' ' spirits of 
salt,' and ' smoking salts.' The pure acid should be colour- 
less, of not less specific gravity than 1*20. It should be 
kept m a cool place. 

Aqua regia. — Called also nitro-hydrochloric acid. This 
is a mixture of one volume of nitric, and from two to three 
of hydrochloric acid. It should not be prepared until 
required to be used, because it decomposes spontaneously. 

Blacklead. — Called also plumbago and graphite. This 
substance always contains a little earthy matter, silica, 
oxide of iron, &c. The most suitable kind is usually very 
black, but without much lustre, until after rubbing. It should 
adhere to the articles, and not become detached when they 
are immersed in the solutions. The best can only be selected 
by means of actual trial, and should be gilded or silvered (see 
p. 217). 

Sulphuretted hydroge/i— Catted also hydric-sulphide. sul- 
phide of hydrogen, &c. This substance is a gas. and may 
'easily be prepared by putting some fragments of prepared 



356 The A rt of Electro- Metallurgy. 

sulphide l of iron (' sulphuret of iron '), into a flask with some 
water, and then adding sulphuric acid. The gas should be 
washed by passing it through a small quantity of water. Sul- 
phuretted hydrogen water is prepared by passing the washed 
gas in bubbles through distilled water until the water is 
saturated. The water dissolves only about three times its 
bulk of the gas ; or one part by weight of the gas dissolves 
in about 250 parts of water. The solution soon decom- 
poses. 

Sulphurous anhydride. — Called also ' sulphurous acid.' 
This is best prepared, by heating in a glass flask, strong oil 
of vitriol, containing fragments of copper wire. The flask 
should be protected from direct contact with the flame by a 
sheet of iron wire gauze. 

Sulphuric acid. — Called also ' oil of vitriol.' The pure 
acid should have a specific gravity of not less than 1-85, and 
be nearly or quite colourless. The least trace of dust or 
organic matter, imparts a darkness of appearance to it, It 
should be kept in a dry place. When diluting it, the water 
should not be poured into the acid, because that is dangerous, 
but the acid into the water, and that slowly (see also p. 

33°)- 

Bisulphide of carbon. — Called also ' sulphuret of carbon/ 
and ' carbon disulphide.' This is a very volatile and inflam- 
mable liquid, and a flame should not therefore be brought 
near its vapour. It should be kept in a well-stoppered or 
corked bottle, in a cool place. 

Phosphorus. — This substance should be kept in a wide- 
mouthed stoppered bottle, filled with water, to keep the air 
from contact with it. The bottle should also be covered 
with black varnish, and kept in a dark place, because the 
light changes the phosphorus and makes it insoluble. Phos- 
phorus should never be exposed to the air for more than a 
few seconds, or it may inflame ; and it should always be 
cut whilst under the surface of water. 

1 Containing one equivalent of sulphur to one of iron. 



Substances used in the Art. 357 

Phosphorus solution. — Called also ' Greek fire.' This 
highly inflammable and dangerous mixture, composed of 
phosphorus dissolved in bisulphide of carbon, has been 
already described (see p. 218). It should only be prepared 
in small quantity ; and the bottle containing it should be 
kept in a cool place, partly immersed in sand, in a stoneware 
vessel covered with a metal lid. It is extremely liable to 
spontaneous combustion, especially if any be spilt. 

Arsenious acid. — Commonly called ' white arsenic' Only 
a small quantity of this is required. The bottle containing 
it should be kept in a dry place, out of the reach of careless 
persons, and should be distinctly labelled ' poison.' 

Antimony. — In purchasing this metal, what is known as 
the ' best star antimony ' should be selected. It may be 
known by its whiter appearance, and by having crystalline 
markings, looking like fern-leaves, upon its surface. 

Bismuth. — This metal varies a little in quality, and is 
liable to contain traces of arsenic, and sometimes also of 
copper. The purer kinds are very much higher in price than 
the common variety. 

Chloride of platinum. — Called also ' platinic chloride,' 
' muriate of platinum,' &c. As the substance sold in shops 
is liable to contain a variable proportion of platinum, it is 
best for the operator to prepare the salt himself, according to 
the directions already given (see p. 118). 

Chloride of gold. — Called also ' muriate of gold,' and 
' auric chloride.' It is better to prepare this than to purchase 
it, because the commercial article is liable to contain a 
variable proportion of gold; it should contain 65*2 percent, 
of that metal (see p. 122). 

Silver. — This metal may be tested for copper, by dis- 
solving it in warm dilute nitric acid, precipitating all the 
silver by means of a slight excess of hydrochloric acid, and 
then adding a drop of solution of ferrocyanide of potassium, 
or by adding ammonia to the solution of argentic nitrate, 
until all the precipitate first formed is re-dissolved. Now look 



353 The A rt of Electro- Metallurgy. 

down through a considerable depth of the clear liquid ; if a 
blueness is visible, copper is present 

Nitrate of silver. — Called also ' argentic nitrate,' ' lunar 
caustic/ &c. It should be in colourless crystals, free from 
odour of nitric acid, entirely soluble in distilled water, and 
should contain 6$\ per cent, of silver. To ascertain the latter 
point, simply melt it at a full red heat, with a little borax in 
an earthen crucible, and weigh the metal ; or precipitate its 
solution by a slight excess of dilute hydrochloric acid, wash, 
dry, and weigh the precipitate; 143^ parts of it equal 108 of 
silver. 

Chloride of silver. — Called also ' argentic chloride/ 'horn- 
silver/ and * muriate of silver.' This substance should con- 
tain 75^ per cent, of silver. To ascertain its percentage, 
melt it, at a full red heat, with an excess of perfectly dry 
(i.e. anhydrous) carbonate of sodium, in an earthen crucible, 
and weigh the button of silver. The chloride is decomposed 
by light, and should be kept in an opaque bottle in a dark 
place. 

Mercury. — Called also ' quicksilver.' Pure mercury is 
perfectly bright, and leaves no tail of drossy appearance, en 
pouring it all slowly out of a vessel : it also volatilises entirely 
by heat. It should be kept in strong bottles, and not allowed 
to come into contact with any metals, except iron, platinum, 
or aluminium. 

Amalgam of gold. — To prepare it, heat pure mercury to 
about 200 C, and add to it the gold in foil or ribbon ; the 
gold is readily absorbed and forms the amalgam. 

Sulphate of copper. — Called also cupric sulphate, ' blue 
vitriol/ 'blue-stone/ 'Roman-vitriol,' &c. The pure salt 
should be in large crystals of a deep blue colour, without 
any admixture of green ; the latter indicates the presence of 
iron. To test for iron, dissolve a little of the salt in distilled 
water, add aqueous ammonia with stirring, until all the blue 
precipitate is re-dissolved. After standing some time, pour 
away the clear blue liquid, add distilled water freely to the 



Substances used in the Art. 359 

residue, and allow it to stand for some time again ; a residue 
of red brown powder, indicates the presence of iron. 

Nickel. — This metal is always contaminated with silicon 
and carbon, which remain as a black powder on dissolving 
the metal in acids. The dried black powder, when fused 
with saltpetre, produces a mixture of silicate and carbonate 
of the alkali. The metal also frequently contains copper \ 
to test for this, dissolve the metal in aqua regia, evaporate 
the solution to a small bulk, dilute with water and add 
sulphuretted hydrogen water; if a blackish cloud is not pro- 
duced, copper is not present. 

Sulphate of iron. — Called also ' green copperas, green 
vitriol,' &c. It should be in the state of clear green crystals, 
perfectly free from adhering water or acid, and with no brown 
or red powder about them. It must be kept dry, and in 
well-closed bottles. 

Carbonate of lead. — Called also ' white-lead/ It is a 
heavy white powder, and should be entirely soluble in warm 
dilute nitric acid ; any white insoluble matter is probably 
sulphate of barium. 

Tin.- — This metal is often adulterated with lead; to 
detect which, cut the tin up as small as possible, digest it with 
warm dilute nitric acid ; evaporate the clear liquid part to a 
small bulk, dilute with water, and add sulphuretted hydrogen 
water ; a black colour or precipitate indicates the probable 
presence of lead or copper. 

Chloride of tin. — Called also ' muriate of tin,' ' tin salt,' 
'butter of tin,' ' stannous chloride,' &c. This should be 
freshly prepared, in nearly dry crystals ; and it should dissolve 
entirely in water, without making the water appear milky. 
The more milky the appearance, the longer has the salt been 
exposed to the atmosphere. 

Caustic lime. — Called also ' lime,' and ' stone-lime.' The 
best quality is perfectly white, and after having been slaked, 
may be rubbed to a soft creamy mixture with water; gritty 
particles consist of silica. Lime should be kept in well- 



3 60 The A rt of Electro-Metallurgy, 

closed jars of stoneware ; if the damp gets in, the lime is 
apt to swell and burst the vessels. Avoid strong building 
limes. These, especially the hydraulic cements, always con- 
tain clay or iron in considerable quantity. 

Carbonate of sodium. — Commonly called 'soda,' and 
'washing soda.' This is usually sold in the form of clear 
colourless crystals, which lose their water, and their trans- 
parency, by exposure to dry air, and fall to a white powder. 
Two hundred and eighty-six parts by weight of the clear 
crystals, require fifty- six parts of pure anhydrous caustic lime, 
to convert them wholly into caustic soda. 

Caustic potash. — Called also ' potash/ and lapis inf emails. 
This substance is sold in several forms, of different degrees 
of purity. It should be kept as much as possible from 
contact with the air, because it rapidly absorbs moisture and 
carbonic acid. A solution of it may be made, by converting 
fifty-six parts by weight of pure and dry caustic lime into 
a cream, by slaking it with water, and then stirring it with 
more water ; adding the creamy mixture to 138 parts of 
anhydrous pearlash dissolved in hot water, and boiling the 
mixture ; the lime subsides to the bottom in the form of a 
carbonate. A purified variety of caustic potash, is sold in 
the form of rods about six inches in length. Great care 
must be taken not to handle it, as it is very caustic, and 
makes most dangerous sores. 

Carbonate of potassium. — Called also ' pearlash,' ' salts of 
tartar/ &c. It is a white salt. Strongly alkaline and de- 
liquescent, and should be kept in well-closed bottles or 
jars. 

Gaseous ammonia. — This substance may be easily pre- 
pared, by separately powdering, and then intimately mixing, 
equal weights of dry caustic lime and sal ammoniac, and 
heating the mixture in a glass flask. 

Aqueous ammonia.— Called also 'volatile alkali/ 'spirit 
of hartshorn/ &c. This liquid is very volatile, and should 
be kept in well-stoppered bottles, in a very cool place. Its 



Substances used in the Art. 361 

specific gravity should not be greater than *SSo. It is danger- 
ous to break the bottles. 

Carbonate of ammonium. — Called also ' smelling salts,' 
' sal volatile.' The unchanged substance is in the form of 
transparent colourless pieces. By exposure to air it loses 
ammonia, and becomes opaque white. It should therefore 
be kept in well-closed bottles. 

Hydrocyanic acid. — Called also ' prussic acid.' This is a 
colourless liquid, consisting of water, more or less impreg- 
nated with the gas. Water will dissolve a very large amount 
of the gas. The strongest usually sold, is known as ' Scheele's,' 
and contains about 5 per cent, of the actual substance ; the 
ordinary medicinal acid contains only 2 per cent. It is 
extremely poisonous, and dangerous to smell or inhale the 
vapour arising from it. It is decomposed by light, and 
should therefore be kept in an opaque bottle, in a dark and 
cool place. 

Cyanide of potassium. — Called also 'prussiate of potash.' 
This substance also is a deadly poison, and almost as 
dangerous when absorbed by the skin, as when swallowed. 
It is strongly alkaline, and abstracts moisture rapidly, and 
should therefore be kept in well-covered jars or bottles. 

Making cyanide of potassium. — As cyanide of potassium 
is extensively used in electro-gilding and electro-deposition 
generally, and especially in making electro silvering baths, 
it is desirable for the practical depositor to understand how 
it is made, and to possess information respecting its im- 
purities, and the method of testing its quality. It is nearly 
always made by the following process : — Take ferrocyanide 
of potassium (yellow prussiate of potash), well crystallised, 
I and free from sulphates ; reduce it to a fine powder, and 
I gently heat it to no° or 120 C. in an iron pan, with constant 
I stirring, until quite dry. Heat to redness a nearly covered 
I iron crucible provided with a lip, put some of the dry powder 
! into it, and when that is melted add some more, and so on, 
i until the crucible is three-fourths filled, keeping the crucible 



362 The Art of Electro-Metallurgy. 

covered as much as possible by means of an iron lid ; gas 
will be evolved freely from the melting salt. Keep the salt 
melted about fifteen minutes, or until the end of an iron rod 
dipped into it shows a white sample. By allowing it to stand 
undisturbed a few minutes at the latter part of the operation 
and occasionally tapping the sides of the crucible, the iron, 
&c. which has separated from the ferrocyanide, will settle at 
the bottom as a fine black powder ; the colourless cyanide 
of potassium may then be poured off into a cold iron pan, 
or upon a thick and cold iron plate ; it should be broken 
up whilst still hot, and preserved in a well-stopped jar. The 
black sediment (which contains much cyanide of potassium) 
should be scraped out of the vessel while still soft, and 
preserved, as water will at any time dissolve the cyanide 
that is in it. 

If the process has been well conducted, the product will 
be of a clear white colour, or at most but very slightly grey. 
The colour, however, is not a matter of importance. To 
prevent oxidation of the cyanide, and consequent formation 
of cyanate of potassium, some operators recommend the 
addition of a few fragments of charcoal, and a little powder 
of the same to the salt, before it is entirely melted. The 
white portion of the product, made according to these instruc- 
tions, contains about 96 per cent, of actual cyanide, and the 
cyanide dissolvable from the black portion, by means of cold 
water, is nearly as pure. To obtain a cyanide of about 70 
or 75 per cent., eight parts of the dried ferrocyanide, mixed 
with three of highly-dried carbonate of potassium, must be 
subjected to similar treatment ; it, however, requires a less 
high temperature for the fusion. By this plan, a larger total 
amount of cyanide of potassium will be obtained, than by 
the fusion of the ferrocyanide only, because in melting the 
latter alone, one third of the cyanogen escapes as gas ; but 
in fusing it with the carbonate, this portion of the cyanogen 
unites with the potassium, and carbonic acid gas escapes in 
its stead. Cyanide of potassium, from which the ferruginous 



Making and Testing Cyanide of Potassium. 363 

matter has not been completely freed, is known as ' black 
cyanide.' Fifty-five parts of crystallised prussiate, become 
forty-eight by drying ; and nineteen of the carbonate, become 
eighteen ; and the sixty-six parts of the dry mixture yield 
about thirty-eight of clean cyanide, besides about six parts 
contained in the black sediment. 

By experiments with the commercial white cyanide, I 
have found, that 200 grains of it would dissolve in 230 grains 
of distilled water at 6o° Fahr., and that it was more soluble 
in water containing hydrocyanic acid. The plan of purifying 
cyanide of potassium from foreign salts, by means of solution 
in alcohol, does not appear to effect the object perfectly. 
Dr. Schwarz recommends the purification of it from carbonate 
and cyanate of potassium, by digesting it in bisulphide of 
carbon, and recovering the solvent by distillation (see 
' Chemical News,' vol. viii. p. 51); but this appears to be 
an unlikely process. 

Testing cyanide of potassium. — According to Glassford 
and Napier, the quantity of pure cyanide in any given sample 
of cyanide of potassium, may be correctly ascertained thus — 
Make two solutions, one of the cyanide, and one of nitrate 
of silver, each containing known weights of the salts, say one 
ounce of the cyanide dissolved in distilled water in a gradu- 
ated glass vessel, so as to form six ounces by measure of 
solution • and 175 grains of the crystallised nitrate, dissolved 
in about two or three ounces of distilled w r ater ; add the 
cyanide solution carefully and slowly to the nitrate of silver 
liquid, with continual stirring, until the precipitate first 
formed is exactly all re-dissolved. The amount of the solu- 
tion required to effect this, with the above quantity of 
nitrate of silver, will have contained 130 grains of pure 
! cyanide, and from the quantity used, we may easily calculate 
j the amount of pure cyanide in the whole ounce. It is said 
l by the authors, that 'when nitrate of silver is added to a 
; solution of cyanide of potassium, so long as the precipitate 
: formed is all re-dissolved, we obtain the whole of the cyanide 



3 64 The A rt of Electro-Metallurgy. 

of potassium in combination with the silver : none of the ! 
other salts in solution take any part in the action, even though 
they be present in a large proportion. This enables us to test 
the exact quantity of cyanide of potassium in any sample.' 

I have employed this process on many occasions, and l] 
have found from 28 to 96 per cent, of actual cyanide in 
different samples. In what is termed ' black cyanide ' I have 
found from 17-65 to 23-40 per cent, of black insoluble 
matter, and of soluble salts, not cyanide, from 5 -2 1 to 5 -43 
per cent., and in a grey specimen 1*35 per cent, of black solid 
matter, and 1875 P er cent, of soluble salts not cyanide. This 
black substance burned in a flame like iron filings, evolved 
an inflammable gas by addition of dilute sulphuric acid ; and 
after digestion in dilute hydrochloric acid, much black com- 
bustible powder was left : it doubtless consists of iron and 
carbon. The other impurities consist of carbonate, sulphide, 
chloride, cyanate, ferrocyanide of potassium, and silica. The 
chloride of potassium is derived from the original salts, and 
the sulphide from sulphate of potassium contained in them ; 
the silica occurs when the cyanide is made in an earthen 
crucible ; and even when the process is well conducted, and 
pure materials used, the product sometimes contains 20 per 
cent, of cyanate of potash, produced partly by the contact of 
the air with the melted mixture. The presence of even a 
small quantity of sulphates in the materials, is said to impart 
to the cyanate, a blue, green, or pink colour ; probably in 
consequence of the production of an alkaline sulphide. 
The price of cyanide varies from about 2s. 6d. to 5*. per 
pound. 

Ferrocyanide of potassium. — Called also ' yellow prussiate 
of potash.' This salt is in the form of large clear yellow j 
crystals, and is used for making the simple cyanide of potas- f 
sium. 

Acetate of copper. — Called also ' crystallised verdigris.' It 
is in the form of dark green crystals, soluble in water. 
Common verdigris is in lumps or powder of a bluish colour, 



Substances, etc., ?tsed in the Art. 365 

and contains a larger proportion of copper, but is Insoluble in 
water : it dissolves in diluted acetic acid, and then forms the 
same liquid as the solution of crystallised verdigris. 

Acetate of lead. — Known also as ' sugar of lead.' It is a 
colourless crystalline salt, with an appearance like that of 
loaf-sugar. It should be entirely soluble in distilled water ; 
if it is not so, add a small quantity of acetic acid (wood- 
vinegar). 

Test-papers. — The most useful variety of these, is neutral- 
tint litmus ; the red and blue kinds may also be employed. 

Thermometers and Hydrometers. — The operator will also 
require a couple of thermometers, and several hydrometers ; 
the latter should be suitable for testing the specific gravity, 
both of aqueous ammonia, and of strong sulphuric acid. 

Syphons. — The most convenient are pieces of tubing of 
glass, gutta-percha, or lead, bent to the proper forms ; or a 
piece of india-rubber tubing. To cause them to act, they 
should be filled with the liquid to be decanted, the ends 
closed by the ringers, and then inverted, with the shortest 
leg plunged into the liquid. 

Filters. — Small ones for filtering dilute acids or alkalies, 
and liquids generally, are made by doubling a circular sheet 
of filtering-paper (i.e. unsized or blotting-paper) twice at 
right angles, opening one of the outer folds, and placing the 
filter in a glass funnel. Large ones are usually formed by 
tying or nailing the edges of a piece of washed or unglazed 
calico to those of a square frame of wood, or of a wooden 
hoop. A filter for strong acids or alkalies, is made by 
placing a loose plug of asbestos in the neck of a glass funnel 
or by filling the neck of the vessel with broken glass, and 
covering the latter with a layer of asbestos. 



2,66 The Art of Electro-Metallurgy. 



REMEDIES FOR ACCIDENTS, ETC., IN PROCESSES OF 
ELECTRO-METALLURGY. 

As various poisonous substances are employed in the art, 
it would be well for the operator to know their best anti- 
dotes. If either nitric, hydrochloric, or sulphuric acid have 
been swallowed, the best remedies are, either to administer 
abundance of tepid water to act as an emetic, or to cause 
the patient to swallow milk, the whites of eggs, some calcined 
magnesia, or a mixture of chalk and water. If those acids 
in a concentrated state, have been spilled upon the skin, 
the parts should be washed with plenty of cold water ; and, 
if necessary, a mixture of whiting and olive-oil then applied. 
A useful mixture for such cases is formed by slaking about 
an ounce of caustic lime with a quarter of an ounce of water, 
then adding it to a quart of water and shaking the mixture 
repeatedly ; decanting the clear liquid, and beating it up with 
olive-oil to form a thin pomatum. Acids spilled upon the 
clothes, should at once be treated with plenty of a quite 
dilute solution of ammonia or its carbonate, and then well 
washed with water. 

In cases where hydrocyanic acid, cyanide of potassium, 
or the ordinary silvering or gilding solutions have been 
swallowed, almost instant death usually follows ; if it does 
not, very cold water should be allowed to run upon the head 
and spine of the sufferer, and the patient be made to swallow 
a dilute solution of either acetate, citrate, or tartrate of iron. 
If the poisoning arises from inhaling the vapour of hydro- 
cyanic acid, cold water should be applied as above, and 
the patient be caused to inhale atmospheric air containing a 
little chlorine gas. It is a dangerous practice to dip the 
naked hands or arms into cyanide solutions, (as workmen 
sometimes do, in order to recover articles which have fallen 
into them,) because those liquids are absorbed by the skin, 



Remedies for Accidents. 367 

and produce poisonous effects ; they also cause very painful 
sores, which should be well washed with water, and the 
mixture of lime-water and olive-oil applied. 

If alkalies, such as potash or soda, have been swallowed, 
a dilute solution of vinegar, some lemonade, or extremely 
dilute sulphuric acid, should be given ; and, after about ten 
minutes, a few spoonfuls of olive oil. 

If metallic salts have been taken, the patient should be 
made to vomit by means of tepid water, and then to swallow 
some milk, whites of eggs, precipitated sulphur, or some sul- 
phuretted hydrogen water. 

To remove stains of sulphate of copper, or of salts of 
mercury, silver, or gold, from the hands, etc., wash them first 
with a dilute solution, either of ammonia, iodide, bromide, or 
cyanide of potassium, and then with plenty of water ; if the 
stains are old ones, they should first be rubbed with the 
strongest acetic acid, and then treated as above. 

Grease, oil, pitch, or tar, may usually be removed from 
the hands, clothes, etc., by rubbing with a rag saturated with 
benzine, spirits of turpentine, or bisulphide of carbon. 



APPENDIX 



LIST OF BOOKS ON ELECTRO-DEPOSITIoN. 

[841. Galvanoplastik Art, by Dr. M. H. Jacobi, translated by \\ . 

Sturgeon. 
[843. Elements of 'Electro-Metallurgy, 2nd Edition. A. Since, F.R.S. 
[844. Manual of Electro-Metallurgy, 2nd Edition. G.Shaw, F.G.S. 
[853. Electro-type Manipulation Part I. 16th Edition, Tart I. 

Edition. C. V. Walker. 
[854. Galvanoplastie. Encyclopedic Korct. 2 vols. Paris. 
[85 5. Theory and Practice of Electro- Deposition. G. Gore. 
[S56. Repertorium der Galvanoplastik und Galvanostcgic. A. Martin. 

2 vols. Vienna : Carl Gerold's Sohn. 
[S62. Les Depots Metalliques. Henri Bouilhet. Paris : Bonaventura 

et Ducessois. 
[S62. De V Orfcvrerie Elcctro-chimique. V. Meunier. Paris \ 
[862. Die Galvanische Vergoldung and Versilberung. W. E. Rab, 

Leipzig : Abel. 
[863. History of Electro- Metallurgy. H. Dircks. 
[866. Elements a" Electro-chimie. M. Becquerel. Paris. 
1S67. Die Galvanoplastik. G. L. v. Kress. Frankfurt am Maine : 

Boselli. 
Katcchismus dcr Galvanoplastik. T. Martius-Matzdorff. Leipzig, 
Die Galvanoplastik. A Hexing. Leipzig : Waldow. 
Electro-chimie. N. A. Renard. Nancy : Lordoillet el I 
Nouvcau Manuel Couplet de Dorurc. Paris : Matthcy el 

Maigne. 
[870. The Elect rotypcrs Manual. Buffalo: W. S. Spiers. 
[872. Galvano-plastic Manipulation. A. Roseleur. 
[873. Kunst des Vergoldens. C II. Schmidt. Weimar: \ 
[873. HydropListic, Electro-chimie, Galvanoplastie. A. de PI 

Paris : Lacroix. 
[874. Electro-Metallurgy, 5th Edition. A. Watt. 

B B 



370 Appendix. 

876. Manual of Electro- Metallurgy, 5th Edition. J. Napier, F. R. S.E. 
876. Handbuch der Galvanoplastik. Von G. Kaselowsky. Stutt- 
garcl : Riegerische Verlagsbuchhandlung. 

878. Journal of Electrotypy, published in Chicago. 

879. Kalechismus der Galvanoplastik. Von G. Seelhorst. Leipzig : 

J. J. Weber. 

880. The Electro-Metallurgist, a periodical. London : Brock & Co. 
880. Stereo-typing and Electro-typing. London : F. T. F. Wilson. 

880. Electro-plating. J. W. Urquhart. 

881. Electro-typing. J. W. Urquhart. 

881. La Galvanoplastie, Electro-chitJiique sur Metaux. G. Marius. 

Orleans : Puget et C ie . 
881. Manuel de Galvanoplastie. Madrid : L. Monet. 
881. Das Galvaniseren von Metallen. W. Pfanhauser. Vienna : 

Lehman n und Wentzel. 
881. Das Verzinnen, Verzinkcn, Vernickeln. F. Hartmann. Vienna : 

Hartleben. 

881. Manuel de Galvanoplastie. Ferrini. Milano : Hoepli. 

882. Electro- Metallurgy. By C. Alker. Brussels : C. Marquardt. 

883. Die Electrolyse, Galvanoplastik und Reinmetallgewinnung. 

Von Edward Japing. Vienna : Hartleben. 
883. Die Galvanoplastik. Von Julius Weiss. Vienna : Hartleben. 
883. ITatechismus der Electrotechnik. Von Th. Schwarze. Leipzig : 

J. J. Weber. 
1883. Die Elektrolyse. Von Dr. Hans Jahn. Vienna : A. Holder. 

In addition to the above there are : — Art of Electro-typing, by 
Sturgeon ; Instructions for the Multiplication of Works of Art by Voltaic 
Electricity, by Spencer ; Manuel Co?nplet de Galvanoplastie, by M. L. 
de Valicourt, 2 vols. ; Traite de Galvano-plastie, by J. L. ; Manuel de 
Dorure et d ' Argenture par la Methode Electro-chimiquc et par Simple 
Immersion, by MM. Selmi and Valicourt. Chapters on electro- 
deposition, in Gmelin , s Handbook of Chemistry, vol. I. Birminghavi 
and Midland Hardware District (Hardwicke), 1865, pp. 477, 510. 
Sprague's Electricity (Spon and Co.), 1875, p. 267. British Manu- 
facturing Industries (Stanford), 1876, p. 137. Applications of the Physical 
Forces, by A. Guillemin, translated by Mrs. Lockyer, 1877, p. 701. 
Also a very large number of original articles on different parts of the 
subject, scattered through the pages of various scientific periodicals, 
to which references have already been made in the body of this book. 



Appendix. 371 



LIST OF PATENTS RELATING TO ELECTRO- 
METALLURGY. 

1836. June 24. G. R. Elkington. Gilding copper, brass, and other 

metals. 

1837. February 17. H. Elkington. Coating metals with gold and 

platinum. 
„ December 4. H. Elkington. Gilding and silvering certain 
metals. 

1838. July 24. G. R. Elkington and O. W. Barratt. Coating copper 

and brass with zinc. 

1840. March 3. J. Shore. Coating metals with copper and nickel. 
„ March 25. G. R. and H. Elkington. Electro-silvering and 

gilding in cyanide solutions. 
,, August 15. No. 8604. V. A. Fontainemoreau. Coating 

metals and alloys with silver, gold, platinum, &c. 
,, October 7. T. Spencer and J. Wilson. Voltaic etching. 
,, December T7. W. T. Mabley. Producing printing surfaces. 

1841. January 14. A. Jones. Making copper vessels. Rendering 

surfaces conductible. 

„ February 8. No. 8842. W. H. F. Talbot. Electrotype and 
photography. 

,, March 8. T. Spencer. Making picture-frames. Depositing 
gold, silver, platinum, and tin. 

,, March 29. A. Parkes. Production of works of art. 

,, September 8. O. W. Barratt. Deposition of copper (from 
mineral waters), silver, gold, platinum, palladium, and 
zinc. 

,, December 9. W. H. F. Talbot. Gilding, silvering, orna- 
menting, &c. Use of alkaline hyposulphites. 

1842. January 15. E. Palmer. Producing printing and embossing 

surfaces (glyphography). 

,, June 1. H. B. Leeson. Electro-depositing processes. ' Gi la- 
tine moulds;' 'positive wires;' 'guiding wires ; ' peeping 
articles in motion; cleaning articles, 'quicking' their sur- 
faces. Claims 430 different salts. 

„ June 4. E. Tuck. Deposition of silver. 

„ August 1. J. S. Woolrich. Plating by means of magi 
electricity. Use of alkaline sulphites. 

„ W. H. F. Talbot. Electro-gilding and silvering. 

B B 2 



372 Appendix. 

1843. April II. J.Napier. Depositing copper upon fibrous materials. 
,, May 4. No. 9720. E. Morewood and G. Rogers. Depositing 

tin upon iron and other metals. 
,, May 25. M. Poole. Plating by means of thermo-electricity. 

Gold, silver, and copper solutions. 
,, June 15. O. W. Barratt. Depositing gold, silver, platinum, 

palladium, lead, &c. 
,, November 21. No. 9,957. A. F. J. Claudet. Producing 

printing surfaces from daguerreotypes. 
,, December 8. J. Schottlaender. Electro-depositing upon felted 

fabrics. 

1844. February 21. No. 10,063. A. Parkes. Deposition of metals 

and alloys. 

»> J u ty 3 1 - No. 10,282. P. A. Fontainemoreau. Electro- 
brassing. 

,, October 22. J.Napier. Depositing metals from fused minerals. 

,, October 29. A. Parkes. Depositing gold and silver from their 
melted salts. 
.845. October 9. A. Parkes. Embellishing metals. 

1846. January 29. No. 11,065. G. Howell. Coating metals with 

platinum. 
„ December 12. L. H. Piagetand P. H. Du Bois. Depositing 
gold, silver, and copper. 

1847. March 23. M. Lyons and W. Mil ward. Bright silver depo- 

sition. 

,, August 3. T. Fletcher. Depositing silver and copper upon 
the backs of glass mirrors. 

,, September 9. J. C. Robertson. Separating sulphur, phos- 
phorus, &c. from melted minerals. 

,, September 30. C. De la Salzede. Deposition of brass and 
bronze upon iron, &c. 

,, November 4. C. M. T. Du Motay. Inlaying metals. 

1848. January 13. S.E.Morse. Production of printing surfaces. 

1849. March 14. P. A. Fontainemoreau. Deposition of platinum, 

gold, silver, copper, brass, tin, and lead. 
,, March 19. T. H. Russell and J. S. Woolrich. Deposition of 

cadmium and of alloys. 
,, March 26. A. Parkes. Depositing printing-rollers, copper, 

silver, bismuth, tin, and lead. 

1850. March 23. A. G. Roseleur. Deposition of tin. 

,, August 9. J.Steele. Gilding, silvering, bronzing, and brassing 
1S51. February 17. C. Cowper. Elastic moulds. 



Appendix. 



373 



1551. May 3. No. 13,620. W. Cooke. Making soda and its car- 

bonate. . 

,, August 23. No. 13,726. J. Palmer. Gelatine moulds for 
electrotype. 

,, September 25. C. Watt. Depositing alkali metals. Sepa- 
rating and purifying metals. 

1552. April 20. J. Ridgway. Coating glass and china. 

,, August 26. A.Crosse. Separating copper from its ores. 

,, October 1. W. Potts. Making sepulchral monuments. 

,, October 2. J. J. Rousseau. Making door-plates. 

,, October 12. F. Michel. Stereotyping in copper. 

,, October 21. J. Bernard. Depositing printing surfaces 

ornamenting leather. 
,, November 13. W. Petrie. Refining metals. 
,, November 29. J. D. Schneiter. Producing maps. 
,, November 30. W. Jeffs. Making letters, figures, &C. 
,, December 11. T. Morris and W. Johnson. Depositing' 

and other alloys. 

,, December II. C. Griffin. Obtaining copper from m 

neral 
waters. 

,, December 28. C. J. Junot. Depositing silicium, tita . 

tungsten, chromium, and molybdenum. 
,, December 29. J. Power. Silvering glass, &c. 
1853. January 1. J. J. W. Watson and W. Prosser. Dej . . 

carbon into iron to form steel. 

,, May 11. W. Bradbury and F. M. Evans. Preparing . 

3 c 3 l & uintin? 

surfaces. 

,, Tuly 29. W. E. Newton. Depositing metals, bronz , 

1 11 r 3 ■ e, brass. 

and an alloy of manganese and zinc. 

,, August 5. No. 1,836. W. Newton. Coating i 

* i j 11 /v t -' on with 

metals and alloys (brass). 

,, October 7. W. Ellis. Ornamenting china and pore 

,, October 8. W. Potts. Ornamenting mantelpieces. 

,, November 7. H. Pershouse and T. Morris. Deposit. 

. .. ung metals 

and alloys. ° 

18^4. Tanuary II. A. R. Brooman. Extracting gold fro 

,, Tanuary 19. G. H. Burrill. Extracting metals fro 

■ , , . 11 » £ 111 minerals, 

slag, and jewellers refuse. 

,, January 30. W. Phillips. Making coffins. 

February 1. R. and J. Jobson. Making mould. 
" ' J J ; for ca ting 

metals. & 

„ February 28. T. Denny. Improvements in eng* 



is 5 r 



374 Appendix. 

1854. March 20. J. Perkins. Making printers' type. 

April 13. G. Devincenzi. Making printing surfaces. 
April 20. J. Reed. Extracting metal from amalgams. 
April 27. C. C. Person. Coating with zinc. 
July 4. J. H. Johnson. Coating iron with lead or copper. 
July 15. M. F. Wagstaffe and J. W. Perkins. Extracting 

metals from their ores. 
July 18. P. A. Fontainemoreau. Etching zinc plates for 

printing. 
July 29. A. E. L. Bellford. Electro-engraving. 
November 4. P. Pretsch. Making copper plates for printing. 
December 21. J. H. Johnson. Making statuettes. 
December 26. F. S- Thomas and W. E. Tilley. Coating 

metals wilh tin, nickel, or aluminium. 
January 3. J. H. Johnson. Coating iron with copper. 
February 3. F. S. Thomas and W. E. Tilley. Deposition of 

silver, copper, nickel, and tin. 
February 13. R. Cornfield. Coating iron with zinc. 
March 17. T. Petitjean and L. Petre. Making daguerreotype 

plates, &c. 
April 2. G. W. Friend. Improvements in umbrellas. 
April 11. L. and A. Oudry. Preserving wood, metal, and 

other substances. 
June 5. F. Puis. Coating iron with zinc. 
July 10. C. J. C. Elkington. Depositing alloys of nickel and 

silver, &c. 
July 21. P. A. Fontainemoreau. Depositing copper upon 
• carbon. 

September 4. J. G. Taylor. Deposition of aluminium. 
"October 4. No. 2,215. H. Cornforth. Electro-coating hooks 

and eyes, 
ctober 12. F. Puis. Deposition of zinc upon iron. 

ctober 25. J. A. Richards. Making embossing surfaces for 

ornamenting leather. 

ivember 14. A. V. Newton. Making surfaces for printing. 

^ cember 3, A. Watt. Coating iron and steel with zinc. 
De 

:ember 6. F. S. Thomas and W. E. Tilley. Depositing 

luminium and its alloys. 

lary I. J. Calvert. Extracting metals from minerals. 

•> ' -J. ary 12. C. Oudry. Preserving metals and other solids. 

-' anu uary 14. E. Morewood and G. Rogers. Deposition of 
Febr 
. vc. 
zir. 



Appendix. 375 

[S56. March 10. L. Chablin and A. Hennique. Ornamenting 

china, &c. 
,, March 25. G. and H. Cottam. Ornamenting chairs and bed- 
steads. 
April 3. J. H. Glassford. Preparing surfaces for printing. 
April 15. No. 899. E. R. Southby. Coating iron with copper. 
June 4. R. A. Brooman. Electro-plating upon glass. 
October 25. G. Ernst and W. Lorberg. Electro-etching. 
December 3. No. 2,871. J. K. Cheatham. Electro-deposi- 
tion with photography. 
December 17. C. Cowper. Deposition of silver and copper 

upon base metals. 
1857. January 1. E. T. Noualhierand J. B. Prevost. Coating glass, 

corpses, &c. with gold, silver, copper, platinum, or iron. 
January 19. J. H. Johnson. Improvements in galvano-plastic 

processes. 
January 22. J. Rubeiy. Electro-brassing the ribs of umbrellas. 
January 27. No. 240. G. T. Bousfield. Coating metals with 

tin. 
March 11. J. D. Cooper. Making printing surfaces. 
March 13. E. J. N. Juvin. Making surfaces for printing. 
March 31. S. Goode. Depositing alloys. 
April 25. J. Burrow. Coating wrought iron with copper 

lead, tin, or zinc. 
April 27. C. Cowper. Depositing gold and silver. 
May 7. D. Morrison. Making printing rollers. 
June 1. W. H. Walenn. Depositing gold, silver, copper, 

bronze, and brass. 
June 24. No. 1,766. A. Parkes. Coating metals with metals. 
July I. W. E. Newton. Producing printing surfaces. 
July 30. S. Coulson. Deposition of aluminium. 
July 30. W. McKinley ami R. Walker. Making moulds ol 

soles of boots and shoes. 
September 21. G. Schaub. Making printing cylinders, 
October 16. J. Chadwick. Making printing rollers. 
December 19. T. Newey, J. Corbett, and W. 11. Pai 

Tinning steel-pens. 
:S58. January 19. No. 93. Otto von Corvin. Inlaying mi I 

menting metals. 
,, February 19. No. 317. J. M. Syers. Extracting metals 

from their ores. 

„ February 22. No. 341. G. Schaub. Making printing types. 



376 Appendix. 



[858. February 23. No. 353. E. C. Shepherd. Depositing metals 
and alloys. 

„ March 12. No. 507. L. F. Corbelli. Deposition of alu- 
minium. 

,, March 22. No. 594. G. Davies. Metallisation of objects 
for electrotype. 

„ March 29. No. 667. E. A. Jacquin. Coating printing sur- 
faces with iron. 

„ April 10. No. 785. A. C. Thibault. Making moulds for 
printing paper-hangin ;S. 

,, April 16. No. 831. J.H.Johnson. Making printing surfaces. 

,, June 3. No. 1,255. Baron Justus Liebig. Protecting backs 
of mirrors. 

,, June 8. No. 1,289. R. A. Brooman. Manufacture of copper 
pipes. 

,, June 22. No. 1,406. G. Schaub. Making door-plates, sign- 
boards, letters, &c. 

,, September 27. No. 2,161. W. Lander. Engraving and 
printing. 

,, October 23. No. 2,371. J. C. Martin. Manufacture of metal 
moulds, &c. 

,, October 28. No. 2,409. W. Munro. Making capsules, &c. 

,, December 16. No. 2,890. R. A. Brooman. Plating and 
gilding forks and spoons. 
:8;9. January 12. No. 103. C. Beslay. Depositing tin, zinc, or lead. 

,, February 5. No. 333. R. Tinkler. Improvements in churns. 

,, February 17. No. 444. B. Saillard. Making printing 
plates. 

,, April 26. No. 1,044. W. Mackenzie. Making printing sur- 
faces. 

,, April 30. No. 1,083. J. Toussaint. Moulds and moulding 
for deposition. 

,, August 29. No. 1,964. G. Edwards. Coating buttons. 

,, September 14. No. 2,095. C. Beslay. Making printing sur- 
faces. 

,, December 6. No. 2,764. F. Potts. Making tubes. 
[860. January 25. No. 187. T. Rampacher and C. F. Schmidt. 
Coating wire gauze. 

,, January 26. No. 204. W. E. Newton. Depositing crystal 
gold. 

,, February 21. No. 469. L. Sautter. Coating mica with 
metal for reflectors. 



Appendix. 377 

i860. March 10. No. 653. T. Morris. Improvements in vats for 
depositing. 

March 22. No. 748. G. T. Peppe. Coating lead with 
tin. 

April 9. No. S93. L. Eidlitz. Producing printing sur- 
faces. 

May 16. No. 1,209. C. M. Guillemin. Coating telegraph 
cables with copper. 

June 6. No. 1,385. E.T.Hughes. Coating type and stereo- 
type. 

June 22. No. 1,523. N. Grattan. Gilding steel and other 
metals. 

July 25. No. 1,800. M. A. F. Mennons. Etching surfaces 
for printing. 

I 1S61. January 7. No. 44. W. Bagley and W. Mincher. Coating 
metals. 

January 19. No. 145. B. Piffard. Preparing non-conducting 
surfaces for deposition. 

Maixh 13. No. 619. J. Cimeg. Silvering glass, &c. 

May 13. No. 1,214. T. Bell. Coating metals with alu- 
minium. 

May 17. No. 1,259. S. Tearne. Producing designs on metal 
articles. 

June 8. No. 1,469. W.Clark. Rendering casks, &c, water- 
tight. 

July 16. No. 1,792. C. D. Abel. Depositing nickel, and 
making alloys. 

August 3. No. 1,936. J. Lewis. Making surfaces for 
printing. 

August 14. No. 2,023. R» A. Brooman. Coating wire with 
gold, silver, copper, &c. 

August 15. No. 2,040. J. Fauchcrre. Making gold 
dials. 

No. 2,314. J. Cimeg. Depositing silver and other metals 
on textile fabrics. 

October 9. No. 2,521. II. B. Coathupe and F. II. Waltham. 
Making embossed surfaces. 

No. 2,675. A. Dalrymple. Depositing metal-. 

October 28. No. 2,699. W.Clark. Producing printing sur- 
faces. 

November 5. No. 2,784. G. T. Bousfield. Depositing metal* 
from concentrated solutions of cyanides. 



$y8 Appendix. 

1861. November 23. No. 2,944. J- Weens. Making metal tubes, 

and coating metals. 
,, December 7. No. 3,074. T. Fearn and T. Cox. Coating 

the metal parts of umbrellas, &c. 
,, December 9. No. 3,081. M. A. F. Mennons. Producing 

designs for printing and embossing, &c. 
,, December 17. J. B. Bunney and T. Wright. Ornamenting 

bedsteads and other articles. 

1862. February 22. No. 469. H. Chavasse, T. Morris, and G. B. 

Haines. Ornamenting bedsteads and other artides. 
,, April 19. No. 149. A. Parkes. Coating surface condensers 

with silver. 
,, May 20. No. 1,528. W. Petrie. Improvements in vessels 

for boiling acids, &c. 
,, May 21. No. 1,538. W. E. Newton. Making metallised 

fabrics or surfaces. 
,, June 28. No. 1,896. C. Beslay. Coating metals. 
,, July 17. No. 2,044. J. Dickson. Making soda. 
,, July 24. No. 2,101. J. Dickson. Extracting copper from 

ores and solutions. 
,, August 12. No. 2,253. J.Dickson. Extracting zinc from ores 

and solutions. 
,, August 12. No. 2,254. J. Dickson. Extracting lead from 

ores and solutions. 
„ August 13. No. 2,265. J- Dickson. Making chlorine. 
,, August 13. No. 2,266. J. Dickson. Deposition of sodium, 

with electrodes of carbon. 
,, August 18. No. 2,314. J. Cimeg. Depositing silver and other 

metals. 
,, August 30. No. 2,410. J. H. Johnson (from C. F. L. Oudry). 

Coating surfaces with copper. 
,, September 9. No. 2,479. J. Maurice. Coating the bottoms 

of ships with copper. 
,, October 3. No. 2,675. A. Dalrymple. Depositing metals. 
,, November 4. No. 2,988. A. Wall. Purifying lead. 

1863. January 20. No. 171. H. A. Bonneville. Ornamenting 

electro-deposited articles. 
,, January 21. No. 180. F. A. Busch. Making vessels for 

containing liquids. 
,, February 25. No. 529. W. E. Newton. Making stereotype 

plates. 
,, March 26. No. 795- G. Davies. Engraving metals. 



Appendix. Z79 

1863. April 21. No. 9S6. H. Rafter. Obtaining printing sur- 

faces. 
,, April 27. No. 1,048. J. J. Robert. Coating spoons and 

forks with silver. 
,, June 24. No. 1,595- T. Skinner. Ornamenting plated 

articles. 
,, August 22. No. 2,088. S. Moore. Improved apparatus for 

electro-plating. 

1864. February 29. No. 497. F.Weil. Coating metals in alkaline 

solutions. 
,, August 15. No. 2,029. S.Moore. Electro-gilding in cyanide 

solutions. 
„ December 14. No. 3,095. J. B. Thompson. Coating iron 

with palladium, platinum, gold, and silver. 
,, December 21. No. 3,164. H. A. de Brion. Varnish for 

electro-plated articles, 

1865. March 10. No. 677. T. Reissig. Electrolysis wiih photo- 

graphy. 

,, May 27. No. 1,457. R. A. Brooman. Producing copies of 
writings, &c. 

,, June 5. No. 1,541. W. E. Newton. 'Photo-electro-typing 
process. ' 

,, July 6. No. 1,791. J. W. Swan. Producing printing surfaces. 

,, August 15. No. 2,110. M. Henry. Electro-type with photo- 
graphy. 

„ October 2. No. 2,521. T.Allan. Preparing iron for electro- 
plating. 

,, October 7. No. 2,592. J. B. Thompson. Depositing iron, 
and coating iron with platinum, gold, silver, and copper. 

,, October 26. No. 2,762. H. Wilde. Apparatus for electro- 
coating. 

,, November 16. No. 2,948. De la Haye. Gilding copper 
wires of telegraphs. 

,, December 23. No. 3,323. E. Clifton. Electro-bronzing. 

,, December 26. No. 3,339. W. F. Deane. Coating the bottoms 
of ships with copper. 

1866. February 14. No. 469. M. Henry. Electro-deposition with 

photography. 

,, April 27. No. 1,186. M.Nelson. Making moulds for electro- 
type plates. 

,, April 27. No. 1,195. J.B.Thompson. Protecting iron ships 
from corrosion. 



380 Appendix. 

1866. May 8. No. 1,315. W. B. Woodbury. Producing designs ! 

upon wood and other substances. 

,, July 25. No. 1,934. C. E. Brooman. Coating armour-plates 
with copper. 

,, August 15. No. 2,095. J' Webster. Coating metals, and 
recovering metals from solutions. 

,, September 28. No. 2,513. W. Clark. Re-producing tele- 
graphic signs and characters. 

,, November 20. No. 3,047. C. E. Brooman. Coating iron 
and steel, with copper and its alloys. 

„ November 26. No. 3,113. R. H. Courtenay. Preparing 
printing surfaces. 

,, December 11. No. 3,517. A. M. Clark. Reduction of tin. 

1867. No. 810. G. Bischof. Coating metals. 
,, April 1. No. 968. C. E. Brooman. Producing surfaces in 

relief. 

1868. May 29. No. 1,777. G. T. Bousfield. Plating spoons, &c. 
,, August 14. No. 2,545. J. B.Thompson. Preparing surfaces 

for gilding, &c. 
,, October 10. No. 3,117. W. R. Lake. Deposition of nickel. 
„ October 15. No. 3,155. H.A.Bonneville. Elastic moulds. 
,, December 15. No. 3,801. A. Watt. Making printing rollers. 
,, December 24. No. 3,930. W. H. Walenn. Depositing 

copper and brass. 

1869. May 12. No. 1,458. P. W. Flower and H. Nash. Coating 

sheets of metal. 
,, July 26. No. 2,268. W. E. Tilley. Coating metals with 

tin. 
„ August 17. No. 2,456. M. H. Jacobi. Depositing iron* 

Forming engraved surfaces, &c 
,,. October 6. No. 2,961. B. Hunt. Ornamenting metals in 

relief. 
,, October 28. No. 3,125. W.Brookes. Deposition of nickel. 
,, October 30. No. 3,159. A. Minton. Coating iron and other 

metals. 
,, November 23. No. 3,377. H. A. Bonneville. Apparatus 

for keeping electrolytes in motion. 
,, December 16. No. 3,643. A. Buirat. Producing engraved 

plates. 

1870. February 2. No. 303. I. Adams, jun. Deposition of nickel. 
,, February 24. No. 554. J. B. Elkington and C. E. Ryder. 

Making copper tubes and rollers. 



Appendix. 381 

1870. April 12. No. 1,068. I. Adams, jun. Preparing surfaces for 

receiving nickel coating. 
„ August 27. No. 2,359. W.R.Lake. Coating tin-tacks with 

copper. 
,, September 28. No. 2,580. J. E. Bingham. Deposition of tin. 
,, November 16. No. 3,005. G. Haseltine. Coating iron with 

gold and silver. 
,, December 30. No. 3,396. E. D. Nagel. Coating iron and 

steel with nickel and cobalt. 

1871. June 8. No. 1,511. H. Wilde. Coating iron boilers with 

copper. 
June 21. No. 1,626. J. Unwin. Deposition of nickel by 

magneto-electricity. Nickel solution. 
July 7. No. 1,777. J- Brough and G. Fletcher. Coating 

vacuum pans. 
August 29. No. 2,266. T. Feara. Depositing alloys of 

nicKel and iron. Solutions for ditto. 
September 16. No. 2,450. W. II. Maitland. Deposition of 

copper. 
October 4. No. 2,623. De Lobstein. Electro-plating. 
December 21. No. 3,459. J. Unwin. Coating with nickel 

by immersion. Solution for ditto. 

1872. May 6. No. 1,376. Fitzgerald and Molloy. Decomposing 

substances with electrodes of carbon. 

June 10. No. 1,742. C. A. Faure. Manufacture of alkalies. 
by electrolysis. 

November I. J. A Jeancon. Deposition of aluminium, 
(N.B. American patent.) 

December 5. No. 3,680. T. Petit jean. Making and orna- 
menting articles. Coating glass, Sec. 

December 18. No. 3,839 J. Noad. Making moulds of sul- 
phide of lead, &c, for electrotype. 

December 31. No. 3,970. J. II. Johnson. Coating iron with 
copper and its alloys. 

No. 95,593. Mr. Unwin. Deposition of nickel. (N.B.French 
patent.) 

1873. February 10. No. 474. R. Werdermann. Reducing metals 

from their ores. 
,, No. 476. R. Werdermann. Reducing metals from their ores. 
,, April 7. T. Fearn. Deposition of tin. 
,, April 29. J. T. Sprague. Galvanometer for use in electrolysis. 
,, July 2. W. R. Lake. Coating iron with nickel. 



382 Appendix. 

1873. December 27. No. 148,459. W. C. Holman. Apparatus to 

show weight of metal deposited. (N.B. American patent.) 

1874. No. 1,492. Brook, Draper, and Unwin. Preparing articles 

for coatings of nickel and other metals. 
No. 1,493. W. Baker and J. Unwin. Deposition of nickel. 
No. 3,033. J. B. Thompson. Coating iron with gold, silver, 

and alloys. 
No. 3,148. W. Morgan Brown. Preparing china and glass 

for being coated. 
No. 3,432. T. S. Johnson. Producing electro-type plates. 
April 19. E. Casselbury. Electrolytic apparatus. (N.B. 

American patent. ) 

1875. No. 58. Wollaston. Thermo-electric apparatus for coating 

metals. 
,, No. 175. Vera. Decomposing water. 
,, No. 473. Clark. Obtaining metals from their salts. 
,, No. 519. Terrell. Electro-typing iron plates. 
„ No. 714. Brown. Producing copper plates and printing 

surfaces. 
,, No. 1,746. Bartlett and Murray. Facing type with nickel. 
,, No. 2,996. Kilner. Magneto-apparatus for electro-coating. 
,, No. 3,243. Alexander. Electro-typing. 
,, No. 3,440. Jewitt. Making gas-burners by deposition. 
,, No. 3,904. Mori. Thermo-regulators for electro-gilding. 
„ No. 4,302. Blewitt. Electro-deposition of tin. 

,, No. 4,326. Ellerbeck and Syers. Making hydrogen and 

oxygen. 
„ No. 4,515. H. Wilde. Refining copper, and coppering 

calico-printers' rollers. 

1876. No. 1,445. Werdermann. Converting metallic salts. 

,, No. 1,704. Fixsen. Compound for galvano-plastic uses. 

,, No. 2,500. Lake. Making wax moulds. 

,, No. 2,554. Prior. Electro-plating with nickel. 

,, No. 2,821. Zanni. Magneto-machine for plating. 

,, No. 2,938. Lake. Galvanic battery for plating. 

,, No. 3,181. Pitt. Making copper tubes, wire, &c. 

,, No. 3,515.' Gardner. Reducing and purifying metals. 

„ No. 3,569. H. Wilde. Electro-coppering rollers. 

,, No. 3,670. Faure. Thermo-battery for coating metals. 

„ No. 4,280. Haddan. Magneto-machine for plating. 

„ No. 4,302. R. J. Blewitt. Coating iron with tin. 

„ No. 4,515. H. Wilde. Making metal rollers. Refining 
copper. 



Appendix. 3S3 

1877. No. 329. Drummond. Producing printing sun 

„ No. 828. Dodd. Electro-plating iron, copper, and nickel. 

„ No. 853. Parkes. Separating nickel from copper in alio; 

,, No. 1,023. Hughes. Electro-plating coils of wire. 

,, No. 1,259. Wiley. Nickel-plating. 

,, No. 1,548. Unwin. Electro-solution of nickel. 

,, No. 1,572. Dupuis and Schultz. Gilding non-metallic frames. 

,, No. 2,996. Kagenbusch and Kerr. Extracting metals from 

slags. 

,, No. 3,476. Lake. Electro-tinning iron plates. 

„ No. 3,743. Johnson. Magneto-machine for electro-metallurgy. 

„ No. 4,053. Lake. Magneto-machine for electro-plating. 

,, No. 4,70s. Lake. Magneto-machine for electro-typing. 

„ No. 4,748. Conradi. Electro metallurgy. 

1878. No. 288. Johnson. Nickel-plating iron wire. 

,, No. 380. Van Winkle. Nickel-plating iron wire. 

,, No. 1,054. Parry. Solution for electro-tinning. 

,, No. 1,228. Wilde. Generating electric currents for use in 
deposition. 

,, No. 1,979. Michaud. Electro-plating with copper. 

,, No. 2,003. Haddan. Machine for electro-plating. 

,, No. 2,017. Keith. Refininglead and separating gold and silver. 

,, No. 2,407. Lake. Making combs by electro-deposition. 

,, No. 3,392. Maxwell Lyte. Coating iron with copper and nickel. 

,, No. 3,425. Maxwell Lyte. Coating iron with copper and nickel. 

,, No. 3,606. Alexander. Etching plates. 

,, No. 3,976. Ward. Magneto-machine for plating. 

,, No. 4,074. Arnaud. Dividing electric currents in plating, 

,, No. 4,075. Johnson. Voltaic battery for electro-plating. 

,, No. 4,206. Higgs. Magneto-machine for depositing metals. 

„ No. 4,313. Cochrane. Generating electricity for electro- 
plating. 

,, No. 4,573. Zanni. Machine for regulating electric currents. 

„ No. 4,611. Edwards and Normandy. Generating electricity 
for electro-plating. 

„ No. 4,755. Cobley. Precipitating copper. 

„ No. 4,921. Lake. Solution for depositing nickel. 

,, No. 5, 127. Glaser. Plating with nickel and cobalt. 

,, No. 5,250. .Scott. Thermo-pUe for depositing metals. 

1879. No. 307. Elphinstone and Vincent Dynamo-machine for 

plating. 

,, No. 359. Brittain. Compound deposit for electro-metalli 

,, No. 529. Blake. Electro-depositing white metal. 



3§4 



Appendix. 



[S79. No. 696. Desmurs. Producing designs on metals. 

Clowes and Batey. Machine for black -leading 



No. 1,203. 
moulds. 
No. 1,387. 
No. 1,481. 
No. 1,592. 
No. 1,692. 



Lake. Dynamo-machines for plating. 
Muller and Geisenberger. Making saltpetre. 
Muller and Geisenberger. Obtaining ammonia. 
Sellon and Edmunds. Regulating currents from 



dynamo-machines for plating. 
2,821. Zanni. Closing and opening circuits during de- 



No. 

position. 
No. 3,565. 
No. 3,586. 
No. 4,087. 
No. 4,100. 
No. 4,295. 
No. 4,821. 
No. 4,862. 

nickel. 
No. 4,879. 

iron. 
No. 5,030. 
No. 5,085. 
No. 5,175. 



Elmore. Dynamo-machine for plating, &c. 
Lambotte-Doucet. Obtaining metals from ores. 
Johnson. Obtaining aluminium and magnesium. 
Lake. Dynamo and batteries for plating. 
Desmurs. Depositing metals for ornament. 
Elmore. Nickel alloys for electro-coating. 
Pitt. Coating insides of provision cans with 

Gutensohn. Separating tin from waste tinned 



Morgan. Producing alkalies and salts. 
Wise. Dynamo-machine for plating. 
Joel. Magneto-machine for plating. 
1880. No. 458. Lake. Extracting metals from ores. 
,, No. 830. Von Buch. Depositing crystalline carbon. 
,, No. 1,120. Parry and Cobley. Coating iron and zinc. 
Dynamo-machine for plating. 
Lake. Dynamo-machine for plating, with regulator. 
Electro-plating wood carvings. 
Electro-typing. 
Producing ammonia. 
Solution for depositing aluminium. 
Etching rollers for printing. 
Separating substances by electrolysis. 
Benzoic acid used in nickel-plating solu- 

Electro-typing inlaid metal articles. 

Decomposing substances by electrolysis. 
Producing designs on printing rollers. 
Electro-plating with copper, nickel, and 

Dynamo-machine for electro-deposition. 
Extracting copper and zinc from liquors. 



No. 


1,178. 


Perry. 


No. 


1,392. 


Lake. I 


No. 


i,556. 


Wirth. 


No. 


i,57o. 


Fischer 


No. 


1,700. 


Young. 


No. 


1,705. 


Davies. 


No. 


1,909. 


Sachs. 


No. 


2,020. 


Abel. 


No. 


2,465. 


Wetter. 


tion. 




No. 


2,519. 


Barlow. 


No. 


2,631. 


Hodge. 


No. 


2,966. 


Sachs. 


No. 


3,043- 


Glaser. 


their alloys. 


No. 


4,005. 


Brewer. 


No. 


4,094. 


Elmore. 



i88o. 



1883. 



Appendix. 



3«s 



Barlow. Producing hydrogen in alcuhol by 



No. 4,541. 

electrolysis. 

No. 4,985. Morgan. Making alkalies by electrolysis. 
No. 6. Chaster. Nickel-plating. 
No. 358. Moss. Electro-typing. 

No. 1,639. Walenn. Deposition of copper, brass, and bronze. 
No. 1,884. Lake. Separating metals from their ores. 
No. 2,875. Giilcher. Producing hydrogen and oxygen by 

gas batteries. 
No. 3,046. Barker. Extracting gold and silver from their ores. 
No. 4,580. Lake. Decomposing alloys by electrolysis. 
No. 5,300. Boult. Electro-plating with nickel and cobalt. 
No. 5,719. Appleton and Horsfield. Nickel-plating engraved 

rollers. 
No. 88. Appleton. Electro-plating metal printing rollers. 
No. 543. Appleton. Electro-plating metal printing plates. 
No. 2,281. Clark. Depolarising electrolytes. 
No. 2,577. Hammersley. Electro-gilding vulcanite. 

Table of useful Numerical Data. 



1 centimetre 


= 


•3937 inches. 


1 decimetre 


. = 


3-937 


1 metre 


. = 


39-37 


I gramme . 


, = 


15-432 grains. 


1 kilogramme . 


. = 


15432- 


1 . 


. = 


35-274 ounces avoirdupois. 


1 ,, . . 


. = 


2-2046 pounds ,, 


I ounce avoirdupois . 


. = 


437 '5 grains. 


I pound ,, 


. = 


7000 • , , 


I pennyweight troy . 


= 


24' 


I ounce troy 


. = 


480- 


I pound ,, . 


• = 


576o- 


1 litre of water . 


. = 


15432- „ 


I 5> 11 


. = 


iooo* grammes. 


I 11 11 


. = 


35-275 ounces by measure. 


I gallon of water 


. = 


4-536 litres. 


1 11 


. = 


70000- grains. 


1 cubic inch of water 


. = 


252-5 „ 


I ounce measure 


. = 


1 -733 cubic inches. 


I pint (or 20 ounces) 


. = 


34-659 » 


I gallon (or 160 ounct 


») . - 


277-276 ,, 


I litre 


. = 


61024 ,, ,, 



c c 



336 



Appendix. 



At the ordinary temperature and pressure of the atmosphere, loo 
cubic inches of — 



Grains 


Grains 


Hydrogen . . weigh 211 


Oxygen . . . weigh 33*80 


Ammonia . ,, i8 - oo 


Carbonic anhydride . ,, 46*50 


Hydrocyanic acid 


Sulphurous anhydride „ 6778 


vapour . . ,, 28-57 


Chlorine. . . ,, 76*40 


Nitrogen . . „ 2970 


Sulphuretted hydro- 


Atmospheric air . „ 31-00 


gen . . . ,, 80-50 



Table of Correspoiiding Temperatures 


on the Scales of 




Centigrade and Fahre?iheit Thermometers. 


Deg. Cent. 


Deg. Fahr. 


Deg. Cent. 


Deg. Fahr. 


Deg. Cent. 


Deg. Fahr. 


100 


212 


66 


150-8 


32 


89-6 


99 


2IO-2 


65 


149 


31 


87-8 


98 


208 -4 


64 


147-2 


30 


86 


97 


206 -6 


63 


I45-4 


29 


84-2 


96 


204-8 


62 


143-6 


28 


82-4 


95 


203 


6l 


141 -8 


27 


80 -6 


94 


20I '2 


60 


I40 


26 


78-8 


93 


199 4 


59 


I 3 8-2 


25 


77 


92 


197-6 


58 


I36-4 


24 


75 '2 


9i 


195-8 


57 


I34'6 


23 


73'4 


90 


194 


56 


132-8 


22 


71-6 


89 


192-2 


55 


131 


21 


69-8 


88 


190-4 


54 


129-2 


20 


68 


87 


188-6 


53 


127-4 


19 


66-2 


86 


186-8 


52 


125-6 


18 


64-4 


85 


185 


5i 


123-8 


17 


62-6 


84 


183-2 


50 


122 


16 


608 


83 


181-4 


49 


1 20 '2 


15 


59 


82 


179-6 


48 


u8-4 


14 


57-2 


81 


177-8 


47 


u6-6 


13 


55-4 


80 


176 


46 


114-8 


12 


53-6 


79 


174-2 


45 


113 


II 


51-8 


78 


172-4 


44 


III -2 


IO 


5o 


77 


170-6 


43 


109-4 


9 


48-2 


76 


168-8 


42 


I07-6 


8 


46-4 


75 


167 


4i 


105-8 


7 


44-6 


74 


165-2 


40 


IO4 


6 


42-8 


73 


i6r4 


39 


I02 -2 


5 


41 


72 


161 -6 


38 


I0O-4 


4 


39-2 


7i 


159-8 


37 


98-6 


3 


37 A 


70 


158 


36 


96-8 


2 


35-6 


69 


156-2 


35 


9S 


1 


33-8 


68 


I54-4 


34 


93-2 





32 


67 


152-6 


33 


91-4 

1 







Appendix. 387 



NOMENCLATURE OF ELECTRICAL UNITS. 

Since the publication of this book, a revision has been made of the 
Nomenclature of Electrical Units. 

The Unit of Resistance is still termed an Ohm, and is equal to that 
offered by 1-0486 metre length of mercury of one square millimetre 
section at o° C. The amount of resistance in a wire, a, is conveniently 
measured by dividing a current from a very small Daniells' cell, so that 
one portion passes through A and one wire, B, of a differential galvano- 
meter, and the other portion through another wire of known resistance, 
C, and the other wire, D, of the galvanometer in the opposite direction 
to that through B, and then the length of A (or of c) altered until the 
needles of the instrument stay at zero ; the resistances of A and C are 
then equal. The measurement of the degree of resistance of an 
electrolyte is much more difficult, on account of the varying polarisation 
of the electrodes. It may be effected in a similar manner, by making 
two measurements by means of a very feeble current after the polarisa- 
tion has become steady : one when the electrodes are near together, 
and the other when they are far asunder, using in each case electrodes 
as large as the transverse section of the electrolyte, and usually of the 
same metal as that of the salt of the liquid. The difference of resistance 
in the two measurements is the amount of resistance of the difference 
of length of the liquid in the two cases. 

The Unit of Electro-motive Force still retains its name of a Volt. 
That of a Daniells' cell is equal to I -070 volt ; and that of a Clarks' 
standard cell is equal to 1*457 volt. For measuring feeble electro- 
motive forces, I have devised a convenient form of thermo-electric 
pile, consisting of about 300 pairs of iron and German-silver wires, and 
have employed it in making a large number of measurements not 
much exceeding that of one Daniell. It is capable of measuring 
differences of ^~- ( ^ of a volt (see ' Proceedings of the Birmingham 
Philosophical Society,' vol. iv. Part 1). 

The Unit of Strength of current is now termed an Ampere, and is 
the strength produced by an electro-motive force of one roll in a 
circuit, having a resistance of one ohm ; it was formerly termed 'one 
Weber per second.' It is that current which will deposit in ;i solution 
of argento-potassic cyanide, containing the least practical amount of 
free cyanide of potassium, "017343 grain of silver per second ; or will 
liberate from dilute sulphuric acid with platinum electrodes, -OOOI02 

C C 2 



388 Appendix. 

grain of hydrogen per second; or will deposit "0051035 grain of 
copper per second from the usual sulphate solution. 

The Unit of Quantity of current is now termed a Coulomb (formerly 
a Weber). It is but little used ; and is the amount which one Ampere 
gives in one second. 

An Unit of Density of current would be of great value in electrolysis, 
but one has not yet been adopted. I have suggested that of one Ampere 
leaving or entering one square centimetre of surface of electrode per 
second (see ' Proceedings of the Birmingham Philosophical Society,' vol. 
iii. p. 277). 



INDEX. 



ACK 
A CETATESof copper and lead, 364, 

. 365 
Acid, acetic, electrolysis of, 29 

— arsenious, 357 

— benzoic, electrolysis of, 96 

— stains, removing of, 367 

Acids, electric relations of metals in, 
table of, 63 

— electrolysis of, 96, 115, 117, 120, 125, 
126, 150, 256, 311 

— first decomposed, 2 

— for batteries, 330 

— for cleaning nicies, 318 

Alkalies, electric relations of metals in, 
table of, 65 

— for cleaning articles, 317 
Alkali-metals, deposition of, 5, 295 

— discovery of, 3 

Alkaline-earth metals, deposition of 

286 
Alloys, deposition of, 50, 272, 278 
Aluminium, deposition of, 289 
Amalgam of gold, 358 
Ammonia, 360 

— electrolysis of, 312 

— gas, preparation of, 360 
Ammonium, deposition of, 305 

— carbonate of, 361 

Analysis of brass by electrolysis, 285 

— copper ores by electrolysis, 213 

— cyanide of potassium, 363 

— dirt from copper anodes, 210 

— silver-plating solution, 175, 184, 186, 
187 

Anions, 34 
Anode, 33 

— of scraps of metal, 230, 343 
Antimony, deposition of, 77, 81, 84, 88, 

99 

— electro-depnsited, properties of, 103 

— selection of, 357 
Antique silver, 181 
Aqua-fortis. 354 

— dipping liquid, 320 
Aqua-regia, 355 



BOO 
Arbor Dianae, 1 
Argentic cyanide, 148 
Argentic chloride and nitrate, 358 
Arsenic, 97 

— hi copper, 31 

— testing for, 98 

— white, 357 
Arsenious acid, 357 
Atomic weights, table of, 42 



TDARIUM, deposition of, 295 

*-* Base metals, deposition of, 198 

gilding, 137, 142, 143 

for electro-plating, preparation of, 

162 
Batteries, exciting liquids for, 330 

— how managed, 335 

— of two metals in one liquid 

— of two metals in two liquii 

— relative power of, 329 
Batten' cells, 334 

— liquids, 330 

— plates, size of, its effect upon the cur- 
rent, 4 

— process for making silver; 
liquid, 165 

— 1 roo irate, 23, 89 

— power, how regulated, 

— relation of action in, to that in depo- 
siting vessel, 74 

■ 
Berzelius notii es electrolytic tr.u 
Binding screws, 1 
Bismuth, 

sition of, 77. 8a, 85, til 
Bisulphide of ci 

in bright plating, 26, 167 
1 . 362 

— lead, rildii 

objects, 

pi 

Blue vitriol. 358 

D, 369 



390 



Index. 



BOR 

Boron, depositions of, 308 

Brass, analysis of by electrolysis, 285 

• — deposition of, 278 

• — first deposited, 25 

— stripping silver from, 183 
Brassing, solution for, 282 
Bright silver-plating, 26, 167 

Brittle negative metals, deposition of, 

97 . 
Bromine, deposition of, 311 
Bronze, deposition of, 272 

— powder, to render surfaces conductive, 

2I 7 
Brugnatelli discovers electro-gilding, 3 

— discovers solution of the anode, 3 
Brunei's brassing solution, 279 
Bunsen's battery, 328 

Busts copied in copper, 227 

— moulding of, 228 



/"""ADMIUM, deposition of, 273 
^-' — salts of. 273 
Caesium, deposition of, 305 
Calcium, deposition of, 293 

— salts of, 292 

Calico-printing rollers produced by de- 

sition, 205, 349 
Carbon, bisulphide of, 356 

— deposition of, 309 
Carbonate of ammonium, 361 

— lead, 359 

— potassium, 360 

— sodium, 360 

Carlisle and Nicholson decompose water, 

2 
Cathode, 34 
Cations, 34 
Caustic lime, 359 A 

— potash, 360 

for cleaning articles, 317 

solution, preparation of, 360 

— soda electrolysed, 151, 297 
Cells, battery, 334 

— number of, its influence upon the 
electric current, 4, 74 

Cement for lining depositing vats, 315 
Cerium, deposition of, 288 
Chemico-electric action, 28 

— relations of substances, 61 
Chloride, argentic, 358 

— of gold and of platinum, 357 

— of silver, testing, 358 

— of tin, 359 

Chlorides decomposed before oxides, 311 
Chlorine, deposition of, 311 
Chromium, deposition of, 252 
Clamond's thermo-electric pile, 353 
Clay figures coppered, 222 
Cleansing metals to receive a deposit, 
315. 3i9 

— silvei, 182 

Cloth coated with copper, 216 
Cobalt, deposition of, 241 



CRTJ 

Coins copied in copper, 224 

— copied in plaster of Paris, 226 

— moulding of, 224 

Coke as a substitute for zinc in batteries, 

68 
Coloured gilding, 138 
Composition for moulding, 225 

— of electro-deposited antimony, 107 
Compound cell apparatus, 34 
Conducting powers affected by tempera- 
ture and purity, 31 

of bodies generally, 28 

— — of metals, 30 

— wires, effect of dimensions of, 32 
Conduction, resistance to, generates 

heat, 31, 32 

Conductors and non-conductors of elec- 
tricity, 29 

Copper, acetate of, 364 

— arsenic in, 31 

— conductivity of, affected by arsenic 
and iron, 31 

— cost of depositing, 210 

— deposition of, 78, 82, 86, 88, 198 
application of, 202 

by means of silicon, 200 

prevented from adhering, 214 

upon non-metallic surfaces, 216 

— electric relations of, 199 

— estimation of, 213 

— extracted from mineral liquids, 203 

— large objects copied in, 229 

— ores, analysis of, by electrolysis, 213 

— plates coated with iron, 246 
etched, 231 

— purity of, its influence on electric con- 
ductivity, 31 

— pyrites, their treatment, 203 

— rapidity of deposition of, 210 

— refined by electrolysis, 212 

— removal from silver articles, 184 

■=- separated from zinc by electrolysis, 285 

— solutions, 207, 247 
— ■ — cyanide of, 207 
management of, 209 

— sulphate of, 358 

Coppering articles of cast iron, 203-221 

— cloth, 216 

— human corpses, 222 

— metals generally, 206 

— plaster and clay figures, 222 

— porcelain and glass, 232 

— fruit, flowers, &c., 221 

— zinc and iron, 208 

Copying busts and statues in copper, 227 

— coins and medals in copper, 224 

— Daguerrotype plates in copper, 215 

— engraved plates in copper, 214 

— set-up type in copper. 223 

— wood engravings in copper, 222 
Corpses coated with metals, 222 
Cream-jugs, how gilded, 143 
Crown of cups, Volta's, 2 

Crude copper by electrodes, purification 
of, 212 



Index. 



39: 



CRU 

Cruickshank, noticed electro-deposition 
of metals, 3 

— his trough hattery, 2 
Crystals of deposited metals, 39 

— — tin, 269 
Cupric sulphate, 358 

Cupriferous mineral liquids, how treated, 

203 
Current, density of, affects the deposit, 

33 

— electric, 71 

— measurement of, 72 

— strength of, 70 
Cyanide, argentic, 148 

— black, 362 

— of copper solutions, 207 

— of gold, 124 

— of mercury, 195 

— of potassium, 361 

analysis of, 363 

impurities in, 364 

preparation of, 363 

— of silver, 148 
Cyanides first employed, 19 

— patented by Elkington and De 
Ruolz, 21 

Cylinders of iron coated with copper, 
205. 349 



D 



AGUERREOTYPE plates copied, 



Dancing and singing mercury, 197 
Daniell's battery, 327 
Davy deposits sodium and potassium, 
297, 299 

— discovers the alkali metals, 3 
Dead gilding, 138 

— silvering, 180 

Debris from copper anodes, 210 
Definite electro-chemical action, 4, 44 
De la Rive, his early experiments in 

gilding, 23 
De la Rue, his observation with a Daniell's 

cell, 4 
De Ruolz, first deposits brass, 25 

— his French patent for the cyanides, 
21 

Density of current, effect of, 38 
Deposited metals, porosity of, 38 
structure of, 38 

— silver, thickness of, 178 
Depositing, by the compound cell appa- 
ratus, 24 

— copper upon glass and porcelain, 232 

— liquids, mishaps in making and using 
them, 341 

accidents and mishaps with, 

34i 

management of, 92, 341 

selection of, 340 

strata and streams in, 55 

testing, 341 

— methods of. 76 

— processes, selection of, 339 



1 I E 
Depositing room, arrangement of, 314 

— several metals in succession, 50, 140 
Deposition, by metals in liquids, Si-87 

— by separate nirru ■ 

— by simple immersion, 77 

— general methods of, 76 

— of alkali-metals, 295 

— of alloys, 50, 272, 278 

— ofmcialN. tir^t observed, 3 

in cyanide solutions, order of, 140 

— of silver, remarkable instance of, 154 

— of tin, remarkable instance of, 265 

— in compound cell apparatus, 90 

— regulation of the, 35-39, 54-55, 74"75. 
90-93. 337. 344-347 

— speed of, 38, 347 

Deposits, adhesion of prevented, 214 

— alloy of, with the cathode, 47 

— circumstances which affect the quality 
of. 35 

— circumstances which affect the quan- 
tity of, 39 

— of copper first observed, 4 

— regulation of, 344 
Didymium, deposition of, 288 
Diffusion in electrolytes, 56 
Dipping liquids, 318 

Dirt, analysis of, from copper anodes, 
210 

— upon anodes of nickel, 239 
Distilled water, 354 
Dyads, 41 



■pARTH METALS, 286 

■*-' Elastic composition, moulds of, 227 

— moulds patented by Dr. Leeson, 25 
Electrical units, nomenclature of, 387 
Electric conducting powers, table of, 

29-31 

— current. 71 

quantity of, conditions of, 4, 72 

regulation of, 337 

— principles of electrometallurgy, 28 

— relations of copj 1 r, 1 ., 

of metals in liquids, 62-69 

of metals in potassic cyanide, 65 

of tin and iron, 

Electri and in- 

sulators of, 29 
Electro-chemical action, 28, 32 

conditions I 

definite, law 

equivalency 

equivalents, determination of, 44 

ol 

Electro-chromy, 260 

Electro-deposited antimony, composition 
of, 107 

properties of, 

bright silvei . f, 169 

iron, uses ami properties of, 248 

nickel, properties .mil use-, of, 240 

metals, purity 

qualiu 



392 



Index. 



ELE 

Electrodes, actions at, 33 

— meaning of the term, 33 

— polarisation of, 54 
Electro-etching, 231 
Electrolysing liquids, force required, 75 
Electrolysis, binary theory of, 45 

— direction of, 35 

— earliest known facts of, 1 

— localities of, 32 

— meaning of the term, 33 

— nomenclature of, 33 

— of acids, 96, 115, 117, 120, 125, 126, 
150, 256, 311 

— of mixed liquids, 50 

— phenomena of, 33, 173, 176 

— rate of, necessary, 36 

— secondary effects of, 46 

— terms used in, 33 

— theories of, 45 

Electrolytes, decomposability of, 34 

— diffusion in, 56 

— direction or electric current in, 35 

— meaning of the term, 33 

— movements in, 55 

— series of, in their order of decompos- 
ability, 34 

Electrolytic movements, 55 

— phenomena, 33, T73, 176 

— transfer first noticed, 3 

— vibrations of mercury, 3, 197 
Electro-metallurgy, books on, 369 

— chemical principles of, 60 

— electric principles of, 28 

— historical sketch of the subject, 1 

— laws and principles of, 28 

— peculiar phenomena in, 176, 215 

— special information respecting sub- 
stances used in the art, 354 

— technical section of the subject, 313 

— theoretical division of the subject, 28 
Electro-motive force, cause of, 70 

' Electro-platers to the trade,' 180 
Electro-plating, early difficulties in, 22 
Electro-type, early experiments in, 5 
Elkington's first experiments in gilding, 

— patent for the cyanides, 21 

— process lor refining copper, 212 
Engraved plates copied in copper, 214 
Etching copper plates, 231 
Explosive deposits, 48, 103 
External resistance, 72 



pARADAY'S discovery of definite 
-*- electro-chemical action, 4 

— discovery of magneto-electricity, 4 

— theory of" electrolysis, 45 
Fearn's tinning solution, 270 
Ferrocyanide of potassium, 364 
Filters and filtration, 365 
Flowers coated with metal, 221 
lluoric a id, 355 See also Hydro- 
fluoric Acid 



Fluorides el ctrolysed, 116, 121, 126, 147, 
150, 300. See alsn Hydrofluoric Acid 

Fluorine, deposition of, 311 

Formic acid, electrolysis of, 96 

French process of silver-plating, 166 

Fruit coated with metal, 221 

Fulminating gold, 123 

Fused fluoride of potassium electrolysed, 
300 

— salts, electrical relations of metals in, 
66,67 

employed for electro-deposition, 

26, 165 

— substances, electric relations of metals 
in, 66 

Fusible alloy, moulds of, 224 



ri ALLIUM, deposition of, 288 
^-* Galvanometer, 62, 73 
Galvano-plastic experiments, 5 
Gas-carbons, 328 
Gases, conduction-resistance of, 31 

— relative weights of, table of, 386 
Gelatine moulds, 227 
Gerboin's experiments, 3, 197 
German-silver deposited, 285 
Gilding base metals, 137, 142, 143 

— black lead, 217 

— by simple immersion, 128 

— coloured, 138 

— correction of colour in, 139 

— first experiment, 3 

— free cyanide in, 140 

— green, 138 

— hot, 136 

— insides of vessels, T43 

— metal dipped bright, 320 

— pink, 138 

— red, 138 

— solutions, 127, 132 

— yellow, 138 

Gladstone's experiments, 37,39, 201 
Glass coated with copper, 232 
Glucinium, deposition of, 292 
Glyphography, Palmer's, 25, 231 
Gold amalgam, 358 

— chloride of, 357 

— cost of depositing, 179 

— cyanide of, 124 

— deposition of, 39, 77, 122 

— methods of punfyin?, 141, 144, 193 

— ornamentation on silver articles, 181 

— pink, 1 38 

— precipitation of, from cyanide solu- 
tions, 144 

— recovery of, from old solutions, 144, 

l8 7 

— removal from silver articles, 184 

— solid deposition of, T36 

— solution, management of, 141 
Golding Eird's experiments, 5, 308 
Gramme's magneto-electric machine, 349 
Graphite, 217, 355 

Grease stains, how to remove, 367 



Index. 



393 



GRE 
Greek fire, 357 

Grotthus's theory of electrolysis, 45 
Grove's battery, 329 
Guiding-wires, 26, 216 
Gutta-percha composition, 225, 315 
moulds of, 2^3 



T I EAT, evolved by conduction-re- 
■*■ ■*■ sistance, 32 

by explosive antimony, 103 

in magneto-electric machines, 50 

Hendersou's process lor extracting 

copper, 204 
Henry decomposes the common acids, 2 
Hexads, 41 

Hisinger notices electrolytic transfer, 3 
Hot coppering solution, 207 

ig, 136 
Hydrochloric acid, 355 

electrolysis of, 95, 117, 125, 311 

Hydrocyanic acid, 361 
Hydrofluoric acid, 355 
electrolysed, 96, 115, 120, 126, 150, 

312 
Hydrogen, absorbed by deposited metals, 

96, 240 
— deposition of, 94 
Hydrometers, 365 
Hyposulphite of silver-plating solution, 

164 



TNDIUM, deposition of, 262 
■*■ Intensity of current, 72 

in relation to number of elements, 4 

Internal resistance. 72 
Iodine, deposition of, 311 
Iridium, deposition of, 114 
Iron, absorption of hydrogen by de- 
posited. 48, 249 

— coated with copper, 207 

— deposition of, 79, 82, 243 

— electric relations of, 264 

— electro-deposited, properties and uses 
of, 248 

— solution, management of, 248 

— strip) ing gold frum, 143 

— sulphate of, 359 



T ACOBI'S galvano-plastic experiments, 

Johnson and Morris's solution for de- 
positing brass, 23 1 

solutiun for depositing German- 
silver. 

Jones's patent for metallising non-con- 
ductors, 25 

Jordan's early experiments in electro- 
type, 5 



I/" LEI N'S process for electro-dcposit- 
■*•*■ ing iron, 246 



MET 

T AMP-POS1 - 1 tated with copper 
J -' 221 

Lanthanium, :'. 288 

Lathe for 51 ratch-l r is ing, 316 
Laws of electro-metallurgy, 28 
Lead, at 

— carbonate of, 359 

ition of, 79, 83, 257 

— white, 359 
Leeson's patent, 25 

Lenoir's process of making copper 

5, 230 
Lime, 359 
Liquids, battery, 330 

— conduction-resistance of, 30 

— depositing, management of, 92, 341 
selection of, 340 

— dipping, 318 

— mixed ones electrolysed, 51 
Lithium, deposition of, 295 
Luckow's process of analysing copper 

ores, 213 
Lunar caustic, 358 



TVf AGNESIUM, deposition of, 286 

Magneto-electric action, dis- 
covered, 4 

first applied in metallurgy, 25 

principle* of, 56, 57 

machines, 347 

by Siemens, 351 

waste of power in, 59,351 

Manganese, deposition of, 249 
Mason's separate battery process, 23, 89 
Measurement of current, 72 
Measures and weights, table of, 381 
Medallions copied in copper, 214 
Mercurial electrodes, sounds produced 
in, 197 

— solutions for quicking, 143, 166, 196, 
323 

Mercury, 358 

-- agitated by electrolysis, 3, 197 

— cyanide of, 

iition of. 78, : 

— first employed to make silver deposits 
adhere. 23 

— recovery of from old zinc . 

I estimating 

in its -..ih-. 
Metal!. 

lead, 

al 

Metallising n m 1 ondu< til 

217. .■)•; 
Metal! l .-6o 

: D Of, 307 

— amount ol electricity produced by 

74 

— base, 

— black de, 



394 



Index. 



MET 

Metals, conducting powers of, 30 

— deposited, cracking of, 37 
crystals of, 38, 39, 269 

quantity of, conditions of, 39, 74, 

345 ,- 
first observed, 3 

— earth, 286 

— electro- deposited, purity of, 49 
quality of, 35 

— in liquids, electric relations of, 62- 
69 . 

— negative, 97 

— noble, 113 

— silvering of, mentioned by Pliny, 
1 

Molybdenum, 255 

Molybdic acid, electrolysis of, 256 

Monads, 41 

Morris and Johnson's solution for de- 
positing brass, 281 

solution for depositing German- 
silver, 285 

Mother-of-pearl copied, 27 

Motion, apparatus for keeping articles 
in, 174 

Moulding busts and statues, 228 

— coins, 224 

— composition for, 225 

Moulds of fusible alloy, wax, gutta- 
percha, 224 

— of plaster of Paris, and elastic com- 
position, 226, 227 

Muriate of gold, 357 

— platinum, 357 

— silver, 358 

— tin, 359 
Muriatic acid, 355 

Murray devises the process of black- 
leading, 23 



TVTAPIER, deposits metals from fused 

■*• ' minerals, 26 

— 's method of analysing silver-plating 

solutions, 187 
Negative electrode, 33 

— meaning of the term, 34 

— metals, deposition of, 94 

— substances set free at the anode, 35 
Nicholson and Carlisle decompose water, 

2 
Nickel, 359 

— deposition of, 82, 232 

— - electro-deposited, properties and uses 
of, 240 

— estimation of, 233, 240 

— first deposited, 21 

— solution, management of, 238 

— testing, 359 

' Nielled silver,' 181 
Nitrate, argentic, 358 

— of silver, testing, 358 
Nitric acid, 354 

testing, 354 



Nitric acid, electrolysis of, 96, 117 
Nitrogen, deposition of, 312 
Nitro-hydrochlonc acid, 355 
Nobili's rings, 4, 260 
Noble metals, deposition of, 113 
Noe's thermo-electric pile, 351 
Nomenclature of electrolysis, 33 
— of electrical units, 387 
Non-conducting surfaces, how rendered 

conductive, 216 
Numerical data, 385 



AHM'S law, 71 

V -^ Oil of vitriol, 356 

• for batteries, 330 

Osmium, deposition of, 113 

Oudry's process for coppering articles of 

iron, 221 
Oxalic acid, electrolysis of, 96 
Oxides decomposed before fluorides, 311 
Oxidised silver, 180 



PALLADIUM, deposition of, 114 
- 1 - Palmer's glyphography, 25, 231 
Pans for acid liquids, 322 
Parkes, deposits metals from fused salts, 
26, 165 

— his solution for solid silver deposits, 
161 

Patents, list of, on electro-metallurgy, 

37i 
Pearlash, 360 
Peroxides formed upon anodes, 4, 55, 

150, 151, 242, 252, 260 
Phenomena of electrolysis, 33, 176, 215 
Phosphorus, 356 

— deposition of, 310 

— moulding composition, 219 

— solution, 218, 247, 357 

— —first used to render surfaces con- 
ductive, 25 

Pink gold, 138 

— silver, 181 

Plaster of Paris figures coppered, 222 

— ■ — moulds of, 226 
Plating balance, 180 

— with silver in melted salts, 165 
Platinic chloride, 357 
Platinised silver, 118, 181 

- its advantages in a battery, 327 

Platinising, 118, 120 
Platinum, chloride of, 357 

— deposition of, 118 
Plumbago, 217, 355 

Poisons and their antidotes, 366 
Polarisation of electrodes, 54 
Polishing paste for silver articles, 182 
Porcelain coated with copper, 232 
Porous cells for batteries, 334 
Positive electrode, 33 

— meaning of the *erm, 35 

— substances set free at cathode, 35 



Index. 



395 



POT 

Potash, 360 

Potassic cyanide, electric relations of, 

65 
how made, 361 

— fluoride electrolysed, 300 
Potassium, carbonate of, 360 

— cyanide of, 361 

— deposition of, 298 
Potential and tension, 71 
Principles of electro-metallurgy, 28 
Prussiate of potash, 361 

yellow, 364 

Prussic acid, 361 
Pyro-plating ; 47, 339 



/^LICKING articles to receive a 
>C deposit, 323 

— process first employed, 23 

— solutions, 143, 166, 196, 323 
Quicksilver, 358 



R 



ED-GILDING, 138 
Reguline state, meaning of the 
term, 36 
Reinsch's test for arsenic, 98 
Resistance, intensity of current, 72 
Rhodium, deposition of, 113 
Roseleur's solution for brassing, 282 

coppering, 207 

— tinning, 270 

Rubidium, deposition of, 305 
Russell and Woolrich's solution for de- 
positing Cadmium, 274 
Ruthenium, deposition of, 113 



C ALTS, table of electric relations of 
^ metals in, 65 _ 

— fused, conductivity of, 30 

— of Tartar, 360 

— smelling, 361 
Sal Volatile, 361 

Salzede's brassing solution, 279 
Scheele's prussic acid, 361 
Schlumberger's process for coppering 

iron cylinders, 205 
Schottlaender's process for coppering 

cloth, 216 
Scrap anodes, 343 
Scratch-brushes, 316 
Screws, binding, 334 
Seebeck discovers thermo-electricity, 4 
Selenium, deposition of, 310 
Set-up type copied in copper, 223 
Shore deposits nickel, 21 
Siemens'* mayneto-electric machine, 351 
Silicon, deposition of, 308 

— deposits silver and copper, 152, 200 
sodium, 297 

Silliman copies mother-of-pearl, 27 



STA 
Silver, antique, 181 

— articles, ornamenting, 1S1 

— chloride of, 358 

— cost of depositing, 179 

— cyanide of, 148 

— deposition of, 77, 82, 85, 146 
bright, 26, 167 

by chemical means, 154 

colour of, 177 

by silicon, 152 

re-dissi living of, 176 

remarkable instance of, 154 

upon cast-iron, 163 

upon wax moulds, 218 

upon soft solder, 164 

Silver, electro-deposited, properties of, 
169 

— first coppered by electro-process, 3 

— its purity tested, 104, 357 

— method of purifying, 194 

— pink, 181 

— plating, French process of, 166 

in France, regulation of, 179 

liquid, composition of, 159 

solution, analysis of, 175, 184, 186. 

187 

bright, preparation of, 167 

made by battery process, 165 

made by chemical method, 156 

strength of, 155 

sulphite of, 153, 164 

— platinised, 118, 181 

— precipitation of, from cyanide solu- 
tions, 144 

— purification of, 194 

— deposited, quality of, 171 

— rapidity of deposition of, 178 

— recovery of, from old solutions, 187 

— removal from copper articles, 183 

— solid deposition of, 161 

— solution, management of, 172-17S 

— stripping copper from, 184 

— stripping gold from, 184 

Silvering solution, free cyanide in, 140, 
175 

— metals, mentioned by Pliny, 1 
Single (ell apparatus, 18 
Smee's battery, 327 

— experiments in electro-deposition, 
=5 

' Smelling salts,' 361 

. ;6b 
St idium, carbonate "f. 360 

— deposition ol by sill, on, 297 
Solid deposition of gold, 136 
of silver, 161 

Sounds produced in mercurial clcctrodt s. 

107 
Spencer's early experiments in clcctrc- 

Spirits "f bail thorn, 360 

— of sail 

Stains, i."« t" remoi 

. J29 

— moulding, 228 



396 



Index. 



STE 

Steel engraved plates copied in copper, 
214 

— rendered brittle by absorbed hydro- 
gen, 49, 97 

Stereotyping in copper, 17, 223 
Stopping-off varnishes, 182, 227, 323 
Strata in depositing solutions, 55, 173 
Streams in depositing solutions, 55 
Stripping articles, 183 
Strontium, deposition of, 294 
Subsalts in deposited silver, 177 
Substances, resistance of, to the electric 
current, 30 

— relative conducting powers of, 29 
Sugar of lead, 365 

Sulphate of copper, depositing solution, 

206 
testing, 358 

— of iron, 359 
Sulphide of carbon, 356 

Sulphite of silver-plating solutions, 153, 

164 
Sulphur, deposition of, 310 
Sulphuretted hydrogen gas, preparation 

of, 355 
Sulphuric acid, 330, 356 
Sulphurous anhydride gas, preparation 

of, 356 
Sulzer mentions the taste of lead with 

silver, 2 
Surfaces, rendering them conductive, 

216 
Syphons, 365 



TARTARIC ACID, electrolysis of, 
9.6 

Tellurium, deposition of, 98 

Temperature, influence of, upon conduc- 
tivity, 31 

Temperatures corresponding, table of, 
386 

Tension and potential, 71 

Testing acids for batteries, 330 

— for arsenic, 98 

— chloride of silver, 358 

— cyanide of potassium, 363 

— depositing liquid, 341 

— nickel, 359 

— nitrate of silver, 358 

— nitric acid, 354 

— silver, 194 

— sulphate of copper, 358 
.— tin, 359 

Test papers, 365 
Tetrads, 41 

Thallium, deposition of, 262 
Thermo-electric action, 59 

— piles, 351 

— series, 60 
Thermo-electricity, discovered, 4 

— employed for deposition, 26 
Thermometers, 365 
Thermometric scales, 382 



Tin, chloride of, 359 

— deposition of, 79, S3, 88, 263 
crystals of, 269 

remarkable instance of, 265 

— electric relations of, 264 

— salt, 359 

— testing of, 359 
Tinning, solution for, 270 
Titanium, 307 

Transference by electrolysis first ob- 
served, 3 

Trees of lead and tin, how formed, 257, 
265 

Triads, 41 

Trinkets for ' dead gilding,' preparation 
of, 139 

Trough, battery, Cruickshank's, 2 

Tungsten, 255 

Type copied in copper, 223 



JJRANIUM, 253 



WALENCY of elements, table of, 41 

— relation of, to electrolysis, 42 
Vanadium, 257 
Varnishes for ' stopping off,' 182, 226, 

323 
Vat, advantages of motion of articles in, 

343 

— silver, arrangement of, 169 

— for containing solutions, 169, 315 

— for depositing, cement for lining, 315 

— motion of articles first adopted in, 26 

— motion of articles, how produced in, I j 
I 7 I ». I .74 

— positions of articles in plating, 343 
Verdigris , 364 
Vitriol, blue, 358 

— green, 359 

Volta's great discovery, 2 

Voltaic batteries, management of, 335 

used in electro-metallurgy, 326 

— currents, source of, 70 
Voltameter, 73 

— first employed, 4 



\^7ALENN'S alkaline coppering so- 
vv lution, 208 

— brassing solution, 284 

— process for depositing iron, 245 
Washing soda, 360 

Wash-waters treated for gold and silver, 

144, 187 
Water, 354 

— first decomposed by electricity, 2 
Watts' brassing solution, 281 

— cyanide of copper solution, 281 

— process for depositing zinc, 277 
Wax moulds, 224, 225 



IlldcX. 



39; 



WEI 

Weighing articles, 1S0 

Weights, atomic, 42 

Weights and measures, table of nu- 
merical data of, 381 

Wiels's process for coppering cast-iron, 
204 

Wilde's magneto-electric machines, 347 

Wireing articles, 325 

Wires for supporting articles in vats, 171 

Wittstein's process fur analysing silver- 
plating solutions, 186 

Wollastun's battery, 326 

— first electro-coats silver with copper, 
3 

Wood engravings copied in copper, 17, 

222 



ZIN 

Woolrich, first applies magneto-electricity 
to plating, 25 

— 's silver-plating - luti 

Woolrich and Russell's solution for de- 
positing cadmium, 274 

Workshop arrangements, 313 

Wrights iir>t employment of alkaline 
cyanides, 19 



7 IXC, 79, 83, 86, 88,274 
'-' — amalgamation of, 332 

— separation from copper by electrolysis 

28 5. 

— estimation of by electroly . 

— selection of, for batteries, 333 



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